A commentary published in Nature this week has opened up a discussion about the value of using the goal of keeping global warming to below 2°C.
David Victor and Charles Kennel are concerned that the below 2°C target for global warming is not useful, partly because they consider it is no longer achievable and partly because global mean surface temperature does not present a full picture of climate change. The problem comes, of course, in identifying an alternative approach to establishing what is required from attempts to mitigate global warming.
The 2 degree target is in a sense nominal, in that it there is no precise threshold at which everything goes from bearable to unbearable, but it does have the advantage of being easy to understand, for both policy makers and the wider public . The proposed alternative indicators, including ocean heat content and high latitude temperature, have scientific validity but the implications of changes in these parameters may not be obvious to people living away from these areas. Furthermore, monitoring any measure on a real time basis will not avoid the intrinsic variability seen in the global temperature record. Ocean heat content shows an apparently unremitting upward trend at present but a climate change denialist would have been happy to point out a “hiatus” in that trend during the 1960s.
Victor and Kennel also state that “the 2°C target has allowed politicians to pretend that they are organizing for action when, in fact, most have done little”. This criticism would apply to any target – providing it is still at such sufficient distance to remain broadly plausible – and their proposal for “a global goal for average [greenhouse gas] concentrations in 2030 or 2050” would provide equal opportunity for prevarication.
According to a review of recent emissions reduction modelling studies conducted for the AVOID 2 programme co-authored by Ajay Gambhir of the Grantham Institute, it is still possible to meet the 2 degrees C target, provided that a broad portfolio of technologies is available and that there are no significant delays in global coordinated mitigation action. A continuation of relatively weak policies to 2030, or the absence of specific technologies such as carbon capture and storage, could however greatly increase mitigation costs and in some models render the target unachievable.
Nevertheless, Victor and Kennel are right to point out the problems with the current over-simplistic approach and I hope that their initiation of a search for “indicators of planetary health” will spur someone to invent a useful new measure for monitoring and assessing climate change.
“Once more unto the breach, dear friends, once more”
Climate change was not, so far as I know, one of the issues that Shakespeare wrote about, despite plays like “The Tempest” or (for the sceptically minded) “Much Ado about Nothing”. But King Henry V’s lines in Act III of the play of that name could have been written for the UN Secretary General to deliver at the Climate Summit in New York on 23 September where, with the help of a VIP cast, he in effect also urged us to “stiffen the sinews” to address one of the defining issues of our age. And he was right to do so.
Without concerted and sustained action to reduce greenhouse gas emissions from the major emitting economies and across various sectors, climate risks will continue to grow to potentially catastrophic levels. Thirteen of the 14 warmest years on record have occurred during the 21st Century. Atmospheric concentrations of carbon dioxide are growing rapidly. And on current trends, the average surface temperature of the planet is likely to be some 4 degrees Celsius warmer by the end of the century.
There is increasing evidence that action on climate change is compatible with continued economic growth and development. Indeed, one could argue that it is a prerequisite. The recent Calderon report illustrates that in many cases action makes sense even in narrow economic terms and highlights the opportunities for action on cities, land use and energy. While undoubtedly there will be losers as well as winners from a transition to a low-carbon economy, this fact has always been true of the major economic and social transformations that have shaped our world.
The point is that, unless we act, there is a real risk that humankind will face a far worse future than its recent past. Financial investors see these risks – that’s why global investors representing US$24 trillion of assets have just called on “governments to develop an ambitious global agreement on climate change by the end of 2015. This would give investors the confidence to support and accelerate the investments in low carbon technologies, in energy efficiency and in climate change adaptation.”
I must admit, the analogy with Henry V is not perfect for (at least) two reasons. First, the venue for the 2015 climate summit that is meant to finalise this new global agreement is Paris. Some six hundred years after the famous battle at Agincourt, I hope preparations for the summit will be marked by excellent co-operation between the UK and France, at all levels!
Second, an all out fight between the developed and the developing world must be avoided. Clearly, whatever agreement is reached in Paris will have to address the diversity of nations and developing country concerns about finance and technology. But the scale of the problem is now such that there can be no rigid divide between the developed and the developing worlds. We will all have to work together if we are to achieve the peak in global emissions in the next ten to fifteen years or so, which is the first necessary step in reducing climate risks.
An international agreement between governments on its own will not be sufficient however. Action needs to be taken at all levels – city, sub-national, national and regional – and across sectors. To quote from the Calderon report, this will only happen if governments provide “consistent, credible, long-term policy signals”. Well-designed policies can drive resource efficiency, create the conditions for investments in low-carbon, resilient infrastructure and stimulate innovation in the technologies we need and the new business models and social practices that will drive this generational transformation to a low-carbon world.
“Once more unto the breach, dear friends, once more”…
The United Nations Climate Summit 2014, to be held in New York on 23rd September, comes at an important point in the calendar for discussions on how to address climate change. Next year will see nations submit pledges on their future greenhouse gas emissions levels, as part of the United Nations process culminating in the 21st Conference of the Parties (COP) in Paris at the end of 2015, the ambition of which is to secure a global agreement to tackle climate change.
There is now a rich body of evidence on the implications of mitigation at the global, regional and national levels. This note presents some of the evidence, revealed by research in the Grantham Institute over recent years, which supports the view that mitigation remains feasible and affordable.
Technologies and costs of a global low-carbon pathway
The Grantham Institute, in partnership with Imperial College’s Energy Futures Laboratory (EFL) demonstrated a relatively simple, transparent analysis of the relative costs of a low-carbon versus carbon-intensive global energy system in 2050. The report concluded that mitigation in line with a 2 degrees Celsius limit to global warming would cost less than 1% of global GDP by 2050 (excluding any potentially significant co-benefits from improved air quality and enhanced energy security).
The two most populous nations, India and China, have undergone rapid economic growth in recent decades, resulting in significantly increased demand for fossil fuels, with associated increases in their CO2 emissions. Mapping pathways towards a low-carbon future for both regions presents challenges in terms of technology choices, affordability and the interplay with land, water and other resources. The Grantham Institute, in partnership with other research groups (including IIASA and UCL), has produced long-term visions of both regions using energy technology modelling and detailed technology and resource assessments, to set out pathways to very low-carbon economies which can be achieved at relatively modest costs. In addition, the Institute has undertaken assessments of the feasibility and cost of achieving the regions’ near-term (2020) Cancun pledges.
Reports have been produced on a number of key technologies across all economic sectors and on the role that these can play in a low-carbon world: electric and other low-carbon vehicles in the transport sector; low-carbon residential heating technologies; other building efficiency and low-carbon options; and a range of technologies and measures to reduce emissions from industrial manufacturing.
The successful development and deployment of a range of low-carbon power sector technologies will be central to decarbonising the power generation sector over the coming decades, thereby providing the basis for low-carbon electrification in the building, transport and industrial sectors. The Institute has produced briefing papers on the technological status, economics and policies to promote solar photovoltaics and carbon capture and storage (including with bioenergy to produce net negative emissions).
A critical consideration in any nation or region’s mitigation strategy is the degree to which a low-carbon transition might put its industries at risk of losing competitiveness against rivals in regions with less stringent mitigation action. In a landmark study using responses from hundreds of manufacturing industries across the European Union, researchers at the Institute, in partnership with the Imperial College Business School and Universidad Carlos III de Madrid, have produced robust evidence to support the contention that the EU’s Emissions Trading System has not produced any significant competitiveness impacts or industry relocation risks.
The energy policies of governments around the world will, to a large extent, determine global greenhouse gas emissions. Western governments cooperate on their energy policies through the International Energy Agency (IEA), which is a powerful advocate and analyst of low carbon energy strategies. Unfortunately the IEA excludes developing nations, such as China, India, Brazil, Indonesia, from its membership. The Grantham Institute is working with China’s Energy research Institute (ERI) to advise the Chinese government on China’s options for greater engagement in international energy cooperation, including closer association with the IEA. China’s participation is important for world energy security and affordability – the other main objectives of energy policy – as well as for climate mitigation. A consultation draft report published by this ERI/Grantham project is at Global energy governance reform and China’s participation. An earlier report by the Grantham Institute with Chatham House is at Global energy governance reform.
The recent slowdown in global temperature rise has led to suggestions that global warming has stopped. In fact, the Earth system is still gaining heat, and the slowdown was likely caused by a series of small volcanic eruptions, a downward trend in the solar cycle, and increased heat uptake of the ocean. Writing in the Telegraph, Christopher Booker claims that a new paper by Professor Carl Wunsch (Wunsch, 2014) shows that ocean warming cannot explain the slowdown because the deeper ocean is in fact cooling rather than warming. Booker is incorrect in his interpretation of the paper, as Professor Wunsch explained in a letter of response to the Telegraph editor that was not published. Wunsch also wrote a letter to the editor of The Australian following a similarly misleading article in that newspaper. There are two threads to Christopher Booker’s argument in the Telegraph article. First, he suggests that the new paper refutes the idea that the pause is caused by an increase in ocean heat uptake, an interpretation that is untrue. Second, Booker gives a misleading interpretation of Wunsch’s appearance on the 2007 television documentary The Great Global warming Swindle in which Wunsch’s views were misrepresented by the documentary makers. Below, I describe the significance of ocean heat uptake and then discuss Booker’s two points in turn.
Figure 1: the amount of heat taken up by the upper ocean (above 700 m), deep ocean (below 700 m), atmosphere and earth, and the amount going into melting ice (IPCC, 2013).
The significance of ocean heat uptake
The ocean is an important heat sink and has taken up over 90% of the extra heat absorbed by the Earth system over the last century. There is natural variation in the amount of heat being taken up by the ocean. This is part of the reason why the observed increase in surface temperatures has not been uniform in the past. All studies including this latest one agree that the ocean above 2000 m is absorbing a significant amount of heat and this is the main focus of studies trying to detect and attribute global warming. The study of the ocean below 2000m is interesting from a scientific point of view but is less relevant to the study of climate change because it takes a very long time for heat to mix to these lower layers. Heat is transferred to the deep ocean by the movement of water masses – the mixing driven by the small-scale movement of water molecules is too slow to be of much significance. Due to the locations of the major ocean currents, parts of the deep ocean such as the western Atlantic and the Southern Ocean in the Antarctic have been in contact with the surface relatively recently, meaning they would be expected to have warmed due to global warming. By contrast, much of the Pacific Ocean below 1500 m has not been in contact with the surface for around a thousand years – something that has been demonstrated by studying the radioactive decay of carbon-14 atoms in a technique similar to the carbon dating of objects (Matsumoto, 2007 – see figure 2).
Figure 2: The circulation carbon-14 age of ocean water below 1500 m (Matsumoto, 2007). Much of the water in the deep Pacific Ocean has not been in contact with the surface for around 1000 years, meaning that its temperature is unlikely to have been influenced by human activities since the industrial revolution.
What is happening in the deep ocean?
Christopher Booker writes, “Prof Carl Wunsch … has produced a paper suggesting not only that the warmists have no real evidence to support their claim other than computer modelling, but that the deeper levels of the oceans have, if anything, not been warming but cooling recently, thanks to climate changes dating back centuries.”
Figure 3: Change in ocean heat content between 1993 and 2011 below 2000 m depth, in units of 108 Joules. There has been heating at this level in the Western Atlantic and Southern Ocean and cooling elsewhere.
In the paper under discussion, Bidecadal Thermal Changes in the Abyssal Ocean, Wunsch looks at observations of ocean heat content. He found that the ocean as a whole and the top 700 m had gained heat since 1993, but that there had been an overall decline in heat content below 2000 m according to the available data. There has been a warming in the regions of the deep ocean below 2000 m where it would be expected due to the transport of water from the surface to the abyss by major ocean currents, i.e. the western Atlantic Ocean and the Southern Ocean (see figure 3). There was an observed cooling below 2000 m in other parts of the ocean including most of the Pacific. Much of the deep Pacific Ocean would not be expected to have warmed due to climate change because the water has not been in recent contact with the surface (figure 2). The available observations are very sparse and only about a third of the water below 2000 m was sampled at all during the period under discussion, meaning it is not known whether these results reflect a genuine cooling below 2000 m. Because there was heating in some places and cooling in others, it is particularly hard to accurately determine the mean from very sparse observations. The main conclusion of Wunsch, 2014 was in fact that more observations are needed to improve our understanding of processes involved in transporting water to the deep ocean. This is a subject which has received relatively little attention, with much more research effort being concentrated on the upper ocean. It is likely that this is partially due to the difficulty involved in observing the ocean at depth, and partly because the upper ocean is of interest due to its direct impact on weather patterns, for example through its role in the formation of El Niño and La Niña conditions. None of this changes the fact that the Earth system as whole is gaining heat, and that a significant proportion of that heat is being taken up by the ocean, mostly in the top 700 m. The paper doesn’t significantly change our understanding of the pause in surface temperature rise. We know that natural processes do change the amount of heat taken up by the ocean over time, and that surface temperature rise has not been uniform in the past. However, precisely quantifying how much heat has been taken up by the deep ocean is still not possible with current observations.
The Great Global Warming Swindle
Referring to the 2007 television documentary, The Great Global Warming Swindle, Booker suggested that Wunsch had privately held “sceptic” views at the time the programme was aired, but didn’t feel able to express these views in public, “So anxious is the professor not to be seen as a “climate sceptic” that, [after being interviewed for] The Great Global Warming Swindle, he complained to Ofcom that, although he had said all those things he was shown as saying, he hadn’t been told that the programme would be dedicated to explaining the scientific case against global warming.” Professor Wunsch’s views on The Great Global Warming Swindle are explained at length on his professional webpage in an article dated March 2007. I will not paraphrase his comments in detail, but suffice it to say he states his belief that “climate change is real, a major threat, and almost surely has a major human-induced component”, and wrote to the documentary makers to say, “I am the one who was swindled” because they misrepresented his views by quoting him out of context. In an update written three months later, Wunsch made it clear that he did not complain to Ofcom under duress from other scientists. In fact, he felt so strongly that his opinions had been misrepresented that he filed his complaint despite threats by the documentary maker to sue him for libel. References Matsumoto, K. (2007), Radiocarbon-based circulation age of the world oceans, J. Geophys. Res., 112, C09004. Wunsch, 2014: Carl Wunsch and Patrick Heimbach, 2014: Bidecadal Thermal Changes in the Abyssal Ocean. J. Phys. Oceanogr., 44, 2013–2030.
There was some good news last week from the annual Petersberg Climate Dialogues held on 14-15 July in Berlin. The Petersberg meetings were instituted after the perceived failure of the Copenhagen summit in 2009 in order to support the UNFCCC talks. They are co-chaired by Germany and the country hosting the next Conference of the Parties meeting, in this case Peru.
Chancellor Merkel took the opportunity in her address to signal renewed ambition for climate action, perhaps disappointing some of those who had been hoping (or even working) for a reversal of Germany’s commitment to decarbonisation. As reported by EurActiv, Merkel said that “A turnaround is needed – worldwide“. Making it clear that she intends to re-energise climate change mitigation, she noted that Germany aims to cut its own CO2 emissions by 40% by 2020 (relative to 1990 levels) and that “Europe will be making an “ambitious contribution” to the forthcoming UNFCCC negotiations that should result in a new climate agreement at the Paris conference in 2015. Of course, the current European Commission proposal to be discussed in October is somewhat less ambitious, reflecting largely East European concerns, and proposes a 40% reduction of EU-wide emissions only by 2030.
The final statement by the German and Peruvian co-Chairs repeated the point I have been making over the past few months to a number of national climate negotiators and the UNFCCC Secretariat and which was the subject of my 3 July blog. This is that “there was a need for [national] contributions in aggregate to meet the overall ambition of maintaining temperature increase below 2°C. In order to ensure this happens, some Ministers acknowledged that a process for collectively considering intended nationally determined contributions was necessary.” Progress, if not yet complete agreement.
The sense of greater momentum was reinforced by the announcement by the Vice President of the Chinese National Development and Reform Commission, Xie Zhenhua, that as part of its contribution to the Paris agreement, it may set a date for the peaking of its own emissions.
Just a couple of months before the UN Secretary General’s climate summit on 23 September, the political climate looks a lot brighter than it has for a long while. Achieving what I see as the first and most significant step on the global mitigation pathway – a peak in global fossil-related carbon dioxide emissions, ideally before 2030 – is the sort of inspirational but realistic target that leaders should now embrace for the Paris agreement if we are to make the most of this opening window of opportunity to limit future climate risks.
In an article for the Telegraph, Christopher Booker gave his views on Professor Sir Brian Hoskins’ appearance on the Today programme earlier this year. In the article, Booker made several claims about climate science relating to rainfall, atmospheric humidity, polar sea ice extent, global temperatures and sea level rise. In this blog I will assess his claims against the findings of the latest report of Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC), a hugely comprehensive assessment of the scientific literature.
Rainfall and floods
Booker’s comment: “Not even the latest technical report from the UN’s Intergovernmental Panel on Climate Change (IPCC) could find any evidence that rainfall and floods were increasing.”
Scientific Evidence:
The IPCC report found a significant climate influence on global scale changes in precipitation patterns (with medium confidence), including increases in precipitation in northern hemisphere mid to high latitudes. Further evidence of this comes from the observed changes in sea level salinity, an indication of the global distribution of evaporation and precipitation. The data is currently too inconclusive to report other regional changes in rainfall with confidence. Overall, however, there had been little change in land-based precipitation since 1900, contrasting with their 2007 assessment, which reported that global precipitation averaged over land areas had increased.
The IPCC concluded that there continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.
The IPCC’s projected short-term changes (2016-35) in rainfall were:
Increased mean precipitation in the high and some of the mid latitudes (very likely)
Reductions in the sub-tropics (more likely than not).
There is also likely to be an increase in the frequency and intensity of heavy precipitation events over land. Regional changes will be strongly affected by natural variability and will also depend on future aerosol level (emissions and volcanic) and land use change.
Global rainfall totals are expected to go up in the longer term (i.e. beyond 2035) by around 1-3% per degree Celsius of global mean surface temperature increase, except in the very lowest emissions scenario.
Booker is partially right on past changes: the IPCC found no significant trend in global average rainfall over land. But this is not to say there has been no effect. Indeed, the expected increase in extreme heavy rain is already happening: the IPCC concluded with medium confidence that since 1951 there has been an increase in the number of heavy precipitation events in more regions than have had a decrease.
Booker’s comment: “From the official National Oceanic and Atmospheric Administration (NOAA) satellite data on humidity (shown on the “atmosphere page” of the science blog Watts Up With That), we see it has actually been falling.”
Scientific Evidence:
The key measure of whether atmospheric humidity is rising or falling is specific humidity, i.e. the mass of water vapour in a unit mass of moist air. The “atmosphere page” of “Watts Up With That” when accessed on 17 July wrongly shows data on relative humidity under the heading “Specific humidity”. Relative humidity is a measure that depends on temperature and does not therefore measure the absolute water vapour content of the atmosphere. In other words, Booker’s evidence is not evidence.
The latest IPCC report concludes that it is very likely that global near surface and tropospheric air specific humidity have increased since the 1970s. However, during recent years the near-surface moistening trend over land has abated (medium confidence). The magnitude of the observed global change in water vapour of about 3.5% in the past 40 years is consistent with the observed temperature change of about 0.5°C during the same period. The water vapour change can be attributed to human influence with medium confidence.
Polar ice melt
Booker’s comment: “As for polar ice, put the Arctic and the Antarctic together and there has lately been more sea ice than at any time since records began (see the Cryosphere Today website).”
Scientific Evidence:
The IPCC found that since 1979, annual Arctic sea ice extent has declined by 0.45-0.51 million km2 per decade and annual Antarctic sea ice extent has increased by 0.13-0.20 million km2 per decade. Taking the two IPCC estimates together, it can be inferred that total global sea ice extent has declined since 1979.
Sea ice thickness is harder to measure. The IPCC combined submarine-based measurements with satellite altimetry, concluding that Arctic sea ice has thinned by 1.3 – 2.3 m between 1980 and 2008. There is insufficient data to estimate any change in Antarctic sea ice thickness.
The reason why the Arctic sea ice has declined and the Antarctic sea ice hasn’t is because they have very different characteristics. Arctic sea ice is constrained by the North American and Eurasian landmasses to the south. In the central Arctic Ocean, the ice can survive several years, which allows it to thicken to several meters. Due to climate warming, the Arctic summer minimum has declined by around 11.5% per decade since 1979, and the extent of the ice that has survived more than two summers has declined by around 13.5% per decade over the same period. This has serious consequences for the surface albedo (reflectance) of the Arctic, as a reduction in the highly reflecting sea ice with less reflective open water results in enhanced absorption of solar radiation.
In contrast to the Arctic, Antarctic sea ice forms in the open ocean with no northern land to constrain its formation. The vast majority of Antarctic sea ice melts each summer.
Booker mentioned sea ice specifically, but he did not mention the other important components of the global cryosphere. Making use of better observations than were available at the time of their previous report in 2007, the IPCC carried out an assessment of all the ice on the planet and concluded that there had been a continued decline in the total amount of ice on the planet. The Greenland and Antarctic ice sheets are both losing mass (with very high confidence and high confidence respectively). Glaciers are known to be declining globally (with very high confidence). Overall snow cover, freshwater ice and frozen ground (permafrost) are also declining, although the available data is mostly for the Northern hemisphere.
Temperature
Booker says: “As for Sir Brian’s claim that by 2100 temperatures will have risen by a further ‘3-5oC’, not even the IPCC dares predict anything so scary.”
Scientific evidence:
Future temperature rise of course depends on greenhouse gas emissions. In the lowest of the IPCC emissions scenarios, which assumes that global carbon dioxide emissions will decline after 2020, reach zero around 2080, and then continue dropping to just below zero by 2090, temperatures are projected to increase by another 0.3oC – 1.7oC by 2100. Total warming under this scenario is projected to be 0.9oC – 2.3oC relative to 1850-1900, i.e. including warming over the 20th century. Under the highest emissions scenario, the closest to business as usual, another 2.6oC – 4.8oC of warming is projected by 2100. In this case, the total projected temperature rise by 2100 is 3.2oC – 5.4oC when past temperature rise is included.
It is worth emphasising that if emissions are not constrained then we are likely to see a temperature rise of the same order as the projections under the IPCC’s highest emissions scenario. All three of the other scenarios assume that carbon dioxide emissions will peak and then decline substantially at some point in the coming decades. If emissions continue to rise then we should expect a total temperature increase in the region of 3.2oC – 5.4oC by the end of the century. This can of course be avoided if action is taken to reduce fossil fuel dependency.
Booker says: “[Professor Hoskins] was never more wobbly than when trying to explain away why there has now been no rise in average global temperatures for 17 years, making nonsense of all those earlier IPCC computer projections that temperatures should by now be rising at 0.3C every decade.”
Scientific evidence:
Figure 1: Past global surface temperature rise according to the MLOST, HadCRUT4 and GISS datasets (IPCC, 2013). There is a long term increase in temperature, but also natural variability.
Climate change is a long term trend, and a few decades worth of data are needed to separate the warming trend from natural variability. Global mean surface temperature increased by about 0.85oC over the period 1880-2012. Each of the last three decades has been warmer than all previous decades in the instrumental record and the decade of the 2000s has been the warmest.
The observed temperature record over the 20th Century shows periods of slower and faster warming in response to a number of factors, most notably natural variability in the climate system, the changes in atmospheric composition due to large-scale human emissions of greenhouse gases and aerosols from burning fossil fuels and land-use change, volcanic activity and small changes in the level of solar activity.
In future, there will continue to be natural variation in temperature as well as a long term warming trend due to our greenhouse gas emissions. Significant natural climate variability means that a prolonged continuation of the current slowdown in the rate of increase would not on its own be strong evidence against climate change, provided that: 1) the global mean sea level continued to rise due to thermal expansion of the oceans, the melting of glaciers and loss of ice from ice sheets, and 2) the measured net energy flow into the climate system (predominantly the ocean) remained significantly positive.
The climate models used by the IPCC are not designed to predict the exact temperature of the Earth surface in a particular year or decade. This would require scientists to predict the future state of climatic phenomena such as the El Niño Southern Oscillation or the Pacific Decadal Oscillation for a specific period several years in advance, something that is not currently possible. Volcanic eruptions also have an impact on global temperatures, and they are not known about far enough in advance to be incorporated into the IPCC’s model projections.
Figure 2: The future projected increase in global surface temperature (IPCC, 2013). All the results are based on several model runs (numbers of model runs shown in the appropriate colours). The red line shows the highest emissions scenario, the closest to business as usual. The dark blue line shows the lowest emissions scenario, which assumes continued reductions in emissions after 2020, and the other two lines (orange and light blue) are intermediate scenarios.
Sea level rise
Booker says: “NOAA’s data show that the modest 200-year-long rise in sea levels has slowed to such an extent that, if its recent trend continues, by the end of the century the sea will have risen by less than seven inches.”
Scientific evidence:
Figure 3: Past sea level rise according to six datasets (IPCC,2013). These are based on tide gauge measurements – satellite data is included after 1993.
The IPCC assessed the relevant data carefully and concluded that sea level rose by around 19 cm (about 7 ½ inches) between 1901 and 2010. This is based on tide gauge data, with satellite data included after 1993. The rate of sea level rise was around 3.2 mm (about 1/8th inch) per year between 1993 and 2010. This is faster than the overall rate since 1901, indicating that sea level rise is accelerating as would be expected from thermal expansion of seawater and increased melting of ice on land.
Future sea level projections under the highest IPCC emissions scenario tell us what is likely to happen if emissions continue to rise unabated. In this case, sea level is projected to increase by a further 63 cm (about 24 ¾ inches) in the last two decades of this century compared with the 1986-2005 average. Even in the lowest emissions scenario, which requires substantial emissions reductions, another 40 cm (about 15 ¾ inches) of sea level rise can be expected by 2100.
IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
Helena Wright, an Imperial PhD student, looks at worst possible scenarios from the IPCC Working Group II report.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC) recently released its latest report, featuring the most up-to-date science on global climate change.
As a researcher, I had an opportunity to contribute to a table in one of the chapters and have read through each of the 30 chapters of the Working Group II report (on Impacts, Adaptation, and Vulnerability). Here is my personal take on seven of the most frightening findings from the WG2 report:
CO2 levels of 1000ppm could impact on mental performance
The health chapter explains how climate change will affect global health, including direct impacts of heat stress, drought and extreme events, as well as indirect impacts on nutrition and mental health.
One extremely frightening direct effect could actually be from CO2 itself. A recent study found indoor CO2 levels of 1000ppm (parts per million) can impair human decision-making performance and cognition. Current atmospheric levels are 400ppm and rising fast. Some scenarios have us reaching these levels by 2100. If these effects are confirmed, how will we be able to adapt?
Climate stress affects children
One particularly frightening aspect of climate change is its impact on children. This is a long term problem with implications for future generations.
Coral reefs would degrade under 2 degrees of warming
The coastal chapter explains carbonate reef structures would degrade under a scenario of 2°C by 2050-2100. Increasing levels of atmospheric CO2 also cause the ocean to acidify, causing coral reefs to lose their structural integrity. The North Atlantic and North Pacific are already becoming more acidic.
Coral reefs are important for biodiversity and account for 20-25% of fish caught in developing countries, as well as housing many other marine creatures. Skeletal “dissolution” is expected to be widespread by 2100. The most frightening thing of all is that these are the impacts under business-as-usual scenarios. Average global temperature has already risen by 0.8°C since 1880. Global leaders have only agreed to limit warming to 2°C of warming, a target they are currently missing.
Climate extremes threaten our food security
Over 70% of agriculture is rain-fed, so agriculture and food security are highly sensitive to changes in rainfall. Higher temperatures have an impact on crop yields. Climate change will affect rivers and oceans as well. Some scenarios forecast widespread fish extinctions in rivers. In one study where data was available, as much as 75% of local fish biodiversity would be ‘headed toward extinction’ by 2070 due to climate change, particularly in tropical areas.
Food price rises triggered by climate shocks disproportionately affect the poor who tend to spend a higher proportion of their income on food.
Global trade will be affected
Climate change will impact on international trade in both physical and value terms. For example, coffee is a major traded beverage which is sensitive to climate variability. Coffee crops will be forced to move to higher altitudes where they are available. Millions of rural people rely on coffee, tea and cocoa production.
The economic costs are expected to be huge. For example, in Ethiopia, agricultural decline is projected to cause a 10% decline in GDP against benchmark levels. While trade can help countries to adapt, for example by importing food, deficits may have to be met by food aid.
Climate change will impact on migration, and could lead to conflict and even wars
High food prices can impact on socio-political stability. For example, 14 countries in Africa experienced food riots in 2008 during the 2008-9 price spike.
People can also be displaced by extreme weather events. But migrants do not necessarily reach safety; with new migrants more at risk at destinations in cities. Sea level rise is projected to lead to permanent displacement as coastal areas become uninhabitable. Under 2 metres of sea level rise, 187 million people are expected to be displaced.
Chapter 12 also examines research on links between climate change and armed conflict. Many of the factors that increase the risk of civil war are sensitive to climate change. US Military experts recently called climate change “a catalyst for conflict”.
There are limits to adaptation
Finally, there are limits to adaptation. This means we cannot adapt to many of these impacts. For example, 31 Native Alaskan villages are facing “imminent threats” due to coastal erosion and several decided to relocate – but their ability to relocate also depends on financial support. Examples of ‘hard’ limits to adaptation include water supply in fossil aquifers, limits to retreat on islands, and loss of genetic diversity. In such cases climate change will lead to irreversible losses.
There are various ‘tipping points’ in the earth system which, if crossed, could trigger rapid and catastrophic climate change. Only mitigation can avoid such risks. Unfortunately little is known about where exactly these ‘thresholds’ lie, making the risks even more difficult to manage.
The limits to adaptation explain why global emission reduction is so vital for humanity. 3-4 degrees of warming would be much more difficult to adapt to than 2 degrees to and could result in the collapse of systems. Yet current climate pledges leave us heading to a world 3.7 degrees warmer. The IPCC shows global emissions are still rising rapidly and show no signs of stabilising. We are entering a radically different world.
However, there are reasons for hope. The UNFCCC negotiations took place again last month in Bonn, with the aim of reaching a global climate deal. There are signs of leadership from the US and China, the worlds’ two biggest emitters, offering renewed hope that collectively we can tackle this problem.
A commentary published in Nature this week has opened up a discussion about the value of using the goal of keeping global warming to below 2°C.
The United Nations Climate Summit 2014, to be held in New York on 23rd September, comes at an important point in the calendar for discussions on how to address climate change. Next year will see nations submit pledges on their future greenhouse gas emissions levels, as part of the United Nations process culminating in the 21st Conference of the Parties (COP) in Paris at the end of 2015, the ambition of which is to secure a global agreement to tackle climate change.
