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Temperature and rainfall extremes in a warming world

heavy rain

By Dr Flora MacTavish

Governments, planning authorities, companies and individuals all need information about  the impact of climate change on extreme weather in the future. A recent paper [1] investigates changes in extremes both globally and locally.

We can be relatively certain of the signature of climate change on a global or continental scale. On the other hand, estimating changes on a country-wide scale is harder and estimating them on a local scale (i.e. to the nearest few kilometres) is very difficult.

In the new study, scientists calculated the proportion of global land area in which certain weather extremes are expected to increase. This can be projected more accurately than the change at an individual location.

The researchers found that the hottest temperatures will get even hotter in half of the global land area within 30 years. This is more useful than simply saying that extreme temperatures will become hotter on average globally. It is also more accurate than making predictions about particular locations.

What impact is climate change having on extreme temperatures and precipitation?

Climate change is already having an impact on the weather we experience. As mean temperatures have increased, the extreme hottest and coldest temperatures have also gone up.

Rainfall patterns have shifted, and there has been an increase in heavy rainfall over most land areas since 1950 (IPCC, 2013).

Globally, these trends are expected to continue over the coming decades. Future trends at a local scale may be obscured by the natural variability of the climate.

Why is this paper interesting?

This study confirms that there are significant uncertainties in how extreme temperature and rainfall will change locally. In some regions, there will probably be no change in extreme weather over the next thirty to fifty years. A small proportion of places may even see a reduction in extreme temperatures or heavy rainfall  events over this time period.

Importantly, these uncertainties are mainly due to the natural variability of the climate. Uncertainties in climate models are much less important. Even a perfect model could not accurately project changes in extremes locally on a thirty to fifty year timescale.

Despite this uncertainty, the study found that it is possible to estimate changes in extreme weather as a proportion of global land area. This technique turned out to be more reliable than making projections for individual regions. It is also more informative than the global average change in extremes.

This technique is not completely new, but the paper adds to a body of research looking at how to predict future extremes.

What does this mean for decision makers?

Reinsurance firms and commodities traders both operate in global markets. They could use this technique to evaluate changes in risk, helping to set premiums or prices more appropriately.

Local planners will probably still opt to build resilience to climate threats. This study does not provide any new information about the impacts of climate change on a local level.

This study does however provide further evidence that it is not possible to predict the pace of change locally. There is little reason to wait for more certainty in the science before beginning to build in greater resilience to extremes.

What methods were used in the paper?

The paper measures the proportion of land that will experience an increase or decrease in extremes. The paper assesses changes in the frequency of:

  • Hot extremes: highest daily maximum temperature in a given year.
  • Cold extremes: coldest daily minimum temperature in a given year.
  • Intensity of heavy precipitation: annual maximum amount of precipitation falling within five consecutive days.
  • Dry spell length: annual maximum number of consecutive dry days, where a dry day has less than 1 mm of precipitation.

Climate models were used to estimate the proportion of global land area in which the above four measures will increase or decrease, and by how much. Firstly, the results of computational simulations using many different climate models were analysed to provide a measure of model uncertainty.

Secondly, the same climate model was run several times with slightly different atmospheric initial conditions. This provided a measure of the uncertainty due to climate variability.

What were the main conclusions?

There are significant uncertainties in how temperature and precipitation extremes will change on a regional scale. These uncertainties are largely due to climate variability, rather than any errors in how models represent climate processes.

The proportion of global land area that will be affected by changes in extremes can be estimated much more reliably. This technique should prove useful to organisations who can make use of global scale information about climate change impacts.

Half of land areas are expected to have hotter temperature extremes within 30 years.

By the period 2016-2035 there is expected to be an increase in the proportion of land areas that will experience intense precipitation.

Further reading from the Grantham Institute

Grantham Briefing Note 1: The slowdown in global mean surface temperature rise

Grantham Briefing Note 5: The changing water cycle

References

[1] Robust spatially aggregated projections of climate extremes, E. M. Fischer, U. Beyerle & R. Knutti.  Nature Climate Change (2013).

[2] 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, in press. Available on the web at: http://www.climatechange2013.org/report/review-drafts/.

China’s carbon intensity reductions continue

By Ajay Gambhir

A fortnight ago a journalist at New Scientist asked me if I’d seen the latest report by the Netherlands Environment Assessment Agency (PBL) and Joint Research Centre (JRC) on last year’s global CO2 emissions figures. He wanted some quick reactions on analysis that showed China’s emissions per unit of economic output (its “emissions intensity”) had declined by over 4% in 2012, compared to 2011 levels. The following analysis is based on my response.

In absolute terms, China’s emissions actually increased by about 3% in 2012, according to the PBL/JRC analysis. But its GDP increased by almost 8% over the course of 2012, so a 3% increase in emissions means between a 4 and 5% decrease in CO2 emissions intensity.

This compares with the 3.5% annual CO2 intensity reduction target in the 12th Five Year Plan, which covers the period 2011-2015 inclusive. 3.5% is the average annual rate of CO2 intensity reductions required over the period 2005-2020, in order that China meets its Copenhagen Accord target (40-45% reduction on 2005 levels by 2020).

What’s particularly interesting is that these reductions have come largely from an increase in renewable energy displacing coal (as opposed, for example, to the offshoring of carbon-intensive industrial output) – lots of hydro, wind and increasingly solar is being deployed in the Chinese power sector. Whilst no form of electricity generation source avoids at least one of the potential problems of local environmental impacts, high costs or variability of output, the increasing share of near-zero-carbon sources in the generation mix gives grounds for optimism in an economy where coal is still dominant (and about 1 coal-fired power station is still being built per week).

However, the challenge to reduce China’s emissions intensity in line with international action that would limit global warming to about 2OC above pre-industrial levels remains a major one. The analysis that I and colleagues at Imperial College and IIASA undertook in 2011 indicated that, if China grew as then projected, with a 6-fold increase in GDP between 2010 and 2050, and its emissions declined to a level of around 3 GtCO2 (equivalent to 1.7 tonnes of CO­2 per person) by 2050, compared to about 8 GtCO­2 in 2010, it would have to reduce its emissions intensity by 6-7% per year on average over that period. This gives an indication of the size of the transformation required.

Also worthy of note is the uncertainty around emissions levels in China. The PBL/JRC analysis has CO2 emissions from fossil fuel combustion and cement rising from about 9.6 GtCO2 in 2011 to 9.9 GtCO2 in 2012, a 3% rise. By contrast the Global Carbon Project’s estimates, released on 18th November, show Chinese emissions rising from 9.1 GtCO2 in 2011 to 9.6 GtCO2 in 2012 – an almost 6% rise. The emissions in these two estimates are not directly comparable, largely because the former includes emissions from international aviation and shipping attributed to China, whereas the latter doesn’t. But estimating emissions is not an exact science (with PBL/JRC noting that there is a 10% range of uncertainty in the Chinese emissions figures), and these two different perspectives tell two different stories.

Nevertheless, during this period of still-strong economic growth it is interesting to see that China’s economy continues to get less carbon intensive. In fact, according to analysis by the UK’s Committee on Climate Change (CCC) earlier this month, China’s CO2 intensity goals for the period 2005 to 2020 mean it is being more ambitious than a range of other countries including the USA and EU27. The challenge now is to meet the 2020 target and then increase the rate of carbon intensity reductions thereafter.

The full New Scientist article is available here.

A different viewpoint on sustainability and development

By Professor Sir Brian Hoskins

Last week the sustainability group of my village and a neighbouring one organised a workshop for local schools. A few of us gave talks, but much of the morning was given to the young people themselves. Each school shared with the group what it is doing on sustainability. The other major activity for them was a debate on whether sustainability and development are compatible. Each school was given two countries that they had to represent in this debate.

Through a contact in Ethiopia and the amazing commitment of a university teacher there, we also had a video to show the young people of a debate on this subject in a class in the University of Mekelle. This video made a deep impression on me. In the western world the focus is often on whether concerns and action on sustainability should be allowed to hold back development. The Ethiopian students turned the topic completely around. They took it as read that they must have sustainability. The debate for them was whether it was possible to also have development!

Perhaps we should be a bit more humble in our discussions of this and similar issues, particularly in a week when we are seeing rich countries blocking effective action to reduce climate risks that will disproportionately affect the less developed.

International Energy Agency announces closer cooperation with developing nations

By Neil Hirst

On Wednesday six major developing nations plus Russia  agreed to pursue closer cooperation, or “Association” with the International Energy Agency. The announcement is superficially modest, but it’s of major strategic importance. It’s the first crack in the “Berlin wall” that has separated energy policy making in the rich OECD countries from that in the developing world. The announcement itself concentrates on making energy markets more efficient but “energy technologies, energy efficiency, and renewable energy” are also on the agenda. These are early days, and there is long way to go to make this initiative effective. But this statement of intention, at Ministerial level, is a new and crucial step.

The IEA, of course, is not a climate change negotiating body. But we will never get international  agreement on climate mitigation until there is a shared understanding of the practical energy policies that can mitigate climate change at the same time as meeting other vital energy policy objectives for security, economic growth, and development. The IEA is where these issues are thrashed out amongst the OECD nations. Now  the major developing countries are , in many ways, some of the most important players. Getting them around the table with the IEA, on an equal basis,  is an important step in coming to grips with  the world’s energy challenges. Developments in Paris yesterday may turn out to be of greater significance than anything that happened at the COP in Poland.

The countries who have joined with the IEA in making this announcement are Brazil, China, India, Indonesia, Russia, and South Africa. There is no certainty where this, initially limited, agreement will lead. But we may be witnessing a first step towards a structure of global energy cooperation that is genuinely fit for purpose.

Question Time and what the IPCC really said about tropical storms

By Dr Simon Buckle

BBC’s Question Time on 14 November saw Lord Lawson citing the IPCC findings to support one of his arguments.  Did I dream that? Then I realised that, of course, the reference to the IPCC was incomplete and misleading so I knew I was awake and back in the strange media-distorted world of the UK debate on climate change.

According to the Daily Express, Lord Lawson said that “If you look at the inter-governmental panel on climate change they say there is absolutely no connection between climate change and tropical storms.” Wrong, but convenient for someone who argues we probably don’t need to do anything much about climate change.

What the IPCC actually said in the admirably cautious Technical Summary of the Fifth Assessment Report (AR5) was that:

“Globally, there is low confidence in attribution of changes in tropical cyclone activity to human influence. This is due to insufficient observational evidence, lack of physical understanding of the links between anthropogenic drivers of climate and tropical cyclone activity, and the low level of agreement between studies as to the relative importance of internal variability, and anthropogenic and natural forcings.”

So far so good for Lord Lawson, but then, the IPCC goes on to say:

“Projections for the 21st century indicate that it is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged, concurrent with a likely increase in both global mean tropical cyclone maximum wind speed and rain rates (Figure TS.26). The influence of future climate change on tropical cyclones is likely to vary by region, but there is low confidence in region-specific projections. The frequency of the most intense storms will more likely than not increase substantially in some basins. More extreme precipitation near the centers of tropical cyclones making landfall are likely in North and Central America, East Africa, West, East, South and Southeast Asia as well as in Australia and many Pacific islands.” (my emphasis).

In making this statement, the IPCC reflects the fact that, while the science is by no means settled, there are a number of studies that provide physical mechanisms linked to climate change that suggest the frequency of the most intense storms would increase with warming.  As I understand it, the warmth of the near surface ocean provides the basic fuel for the cyclone: the winds spiralling around the system evaporate water which cools the ocean and puts latent heat into the atmosphere. When the air rises and the water condenses in deep convection in the storm the heating leads to extra ascent, drawing in more air and leading to faster surface winds. The warmer the ocean is, the more fuel there is for a potential tropical cyclone, and the stronger they could be. Many other aspects come into play such as the changing winds with height and the temperature of the atmosphere up to 15 km. However, in a warmer world, the potential for stronger storms is there.

Indeed, based on this sort of evidence, the quote highlighted above is a statement that the IPCC judges there is more than a 50% chance that the frequency of the most intense storms will increase substantially in some ocean basins.  So if Typhoon Haiyan was not affected by climate change and yet was still one of the most powerful storms ever making landfall, it’s clear that the Philippines and other regions exposed to tropical cyclones have a lot to worry about unless we make a “substantial and sustained reductions of greenhouse gas emissions (SPM Section E).” It would be good to see Lord Lawson quoting that particular part of the IPCC AR5 report!

Updates to the IPCC WG1 Summary for Policy Makers

By Dr Flora MacTavish

The IPCC has released corrected figures for past carbon dioxide emissions and future emissions trajectories quoted in the Summary for Policy Makers of the Working Group 1 report, “Climate Change 2013: The Physical Science Basis”.  The original numbers were published in the report released on 27th September, which was subject to copy edit and final layout changes.

In total, six values from the summary have been changed. As noted by Professor Sir Brian Hoskins, Director of the Grantham Institute, these corrections are minor adjustments to historical greenhouse gas emissions and to the cumulative emissions consistent with achieving a 2 degree warming target with different levels of probability.  The 2 degree target is significant because it forms the basis of international climate change negotiations. These minor corrections do not affect any of the conclusions drawn in the Summary for Policy Makers.

Since the IPCC did not do so, I have produced the following table to compare the new values to the original values for all the parameters that have changed. For each parameter, the difference between the original best estimate and the new best estimate is given in the right hand column. This is also expressed as a percentage of the original value.  As can easily be seen, the changes in the parameters are all relatively small compared to the values of those parameters. Most are also small compared to the 90% uncertainty interval (range) given.

If you are unable to read the table below you can also view it here.

Section of the SPM affected Parameter changed Value given in the version released on 27th Sep 2013 (gigatonnes of carbon, GtC) New values, released 11th November  2013 (all in gigatonnes of carbon, GtC) Comment
Section B.5, bullet 4 Cumulative CO2 emissions from fossil fuel combustion and cement production over the period 1750 to 2011. 365 [335 to 395] 375 [345 to 405] The best estimate and range revised upwards by 10 GtC, an increase of 2.7% in the best estimate.
Section B.5, bullet 4 Cumulative anthropogenic CO2 emissions over the period 1750 to 2011. 545 [460 to 630]  555 [470 to 640] Best estimate and range revised upwards by 10 GtC, an increase of 1.8% in the best estimate.
Section B.5, bullet 5 The accumulation of carbon from anthropogenic CO2 emissions in natural terrestrial ecosystems over the period 1750 to 2011. 150 [60 to 240] 160 [70 to 250] Best estimate and range revised upwards by 10 GtC, an increase of 6.7% in the best estimate.
Section E.8, bullet 2 Total cumulative CO2 emissions from all anthropogenic sources to limit warming to less than 2°C (from CO2 alone) since the period 1861–1880 with a probability of >33%. 0 to 1560 0 to 1570 The maximum value was revised upwards by 10 GtC, a percentage increase of 0.64%.
Section E.8, bullet 2 The maximum cumulative CO2 emissions from all anthropogenic sources for limiting warming to less than 2°C (including non-CO2 forcing as in RCP2.6 – the lowest emissions scenario used by the IPCC) listed for probabilities of >33%, >50%, and >66%. 880, 840 and 800  900, 820 and 790 Numbers changed by +20, -20 and -10 GtC. The percentage changes were +2.3%, -2.4% and -1.3%.
Section E.8, bullet 2 Cumulative anthropogenic CO2 emissions over the period 1870 to 2011. 531 [446 to 616] 515 [445 to 585] Best estimate reduced by 16 GtC, a decrease of 3%. Range also reduced from 170 to 140 GtC.

 

 

The future of our planet is far too important to be left just to our politicians

By Dr Simon Buckle

Two years to go and counting down. That’s the real significance of COP19, the Warsaw Conference of the Parties of the UN Framework Convention on Climate Change (UNFCCC), which runs from 11-22 November. A new universal climate agreement effective from 2020 is what is at stake, and Warsaw is a step on the path.

The COP21 meeting in Paris at the end of 2015 will hopefully be the successful culmination of many years’ of hard work by the UNFCCC Secretariat, government climate negotiators and many, many others. It’s time for governments to act on the words they agreed in the IPCC Summary for Policy Makers launched on 27 September – namely that substantial and sustained reductions in emissions are required to limit climate risks.  No doubt this is a point Ban Ki-Moon will make at his planned high-level Climate Summit in September 2014.

So how important is the Warsaw COP in this packed schedule to Paris? According to Christiana Figueres, the Executive Secretary of the UNFCCC Secretariat based in Bonn, the meeting is “a pivotal moment to advance international climate action and showcase a growing momentum to address climate change at all levels of society”.  That’s why there’s a Business Forum and a “Cities Day”.  There is also a Gender Day to showcase women’s role in meeting the climate challenge – a very welcome initiative since the differential impacts on distinct societal groups with contrasting interests and values is at the core of how we decide to respond – or not – to climate change.

Climate change is a critical issue for business, and business has to be part of the solution.  Companies realise that they can both become more profitable and improve business resilience by taking climate change and energy efficiency seriously.  We need to scale up these efforts significantly to limit the risks from climate change. The car industry is a good example of where European emissions regulation has encouraged innovation to reduce emissions.  However, businesses often have shareholders as well as customers and there is only so much they can do without a clear policy framework, a meaningful carbon price to capture the damage emissions do to others and adequate incentives for innovation and investment in clean technologies and new businesses, rather than in the old economy.

There is also a growing recognition that there are clear benefits, even in the short-term, from tackling climate change, including greater energy security.  Cities as key concentrators of human, financial and physical capital and resource use are at the forefront of efforts to make the transition to a lower impact and more resilient way of life. In rural areas, renewable technologies can play a valuable role in extending energy access for poor people in developing countries – a role that will grow as technologies get better and cheaper.

But Warsaw has to be about more than just showcasing what could be if we really tried.  To create the political conditions for an ambitious and effective mitigation agreement in 2015 covering all the major emitters, there’s a huge amount of hard work still to be done.  Warsaw can contribute by helping mobilise governments to deliver an ambitious and effective climate agreement in Paris in 2015.  Well before the end of next year, we need all the major emitting economies to have put on the negotiating table national commitments to significant and verifiable emissions reductions beyond 2020, with the degree of effort tailored to particular national circumstances.  This is not like the Kyoto Protocol. Emissions reductions are needed from developing as well as developed economies; the climate doesn’t care where the emissions come from.

Of course, vulnerable, developing economies will need help to make the transition to low-carbon, resilient economies. So a successful outcome in Paris depends on the quantity and quality of financial, technological and adaptation support that the UNFCCC institutions can mobilise for these countries.  Warsaw will hopefully take decisions to make the Green Climate Fund, the Technology Mechanism and the Adaptation Committee fully operational.  But institutions are not enough in themselves.  The developed economies have to deliver on their promises of additional financing. Clarity on plans to scale up finance to 2020 will be critical to success in Paris in 2015.

The great advantage of the UN process in tackling climate change is that it brings together over 190 countries with very diverse capacities and perspectives in a sustained effort to create an effective global response to climate change.  The voices of the poor and vulnerable can be effective in putting moral pressure on the rich.  The UNFCCC process should help us avoid a situation where the climate risks faced by the majority are determined by the decisions of the few.

This strength is of course also the UNFCCC’s Achilles Heel.  International agreements cannot bind national governments if they don’t want to be bound.  So whatever is agreed at Paris can only be as ambitious as countries judge is in their own interest, taking account of what others are doing in their self interest.  This is why there have been persistent calls for “bottom-up” approaches. While focused groupings, like the Major Economies Forum, can make a valuable contribution to the process, we need the UN process to keep up the pressure and also to provide an independent mechanism for monitoring, reporting and verifying countries’ emissions reductions.

As we’ve seen with the national pledges made after the Copenhagen COP, an agreement in Paris that is based purely on what countries want to do is unlikely to meet the scale of the challenge. Time is short, perhaps 50 years to make the transition to a much lower carbon world.  This is why the UNFCCC is absolutely right to seek to involve a much wider range of non-governmental actors in the discussions at Warsaw and beyond, to try and raise the level of ambition and to redefine what is feasible.

The future of our planet is far too important to be left just to our politicians.

 

Transient Climate Response: an incomplete measure of climate change

By Dr Simon Buckle

It may help to clarify some of the facts related to the lively exchange between Bob Ward and Lord Ridley about the Transient Climate Response (TCR). The TCR is defined by the IPCC as “the change in the global mean surface temperature, averaged over a 20-year period, centred at the time of atmospheric carbon dioxide doubling, in a climate model simulation in which CO2 increases at 1% yr – 1.”

Lord Ridley is right that the IPCC in its recently published AR5 Working Group I report gave an estimated likely (66–100% probability) range for TCR of 1 – 2.5°C.  The IPCC also increased its confidence that the TCR is not greater than 3.0°C though it is not immediately clear what confidence the IPCC places on the 1°C lower limit, rather than the range it provides.

As Bob Ward notes, however, the TCR is unlikely to reflect how global mean surface temperatures might increase during this century, as claimed by Lord Ridley. This is for two reasons. First, our carbon dioxide emissions are rising by around three percent not one percent per year.  Second, the TCR only refers to changes due to carbon dioxide; climate change will be greater than this due to increases in other greenhouse gases such as methane and nitrous oxide, though it is also offset to some degree by atmospheric aerosols.

Our current emissions are broadly in line with the most emissions intensive of the IPCC’s scenarios for AR5 – the so-called RCP8.5 scenario.  This is likely to lead to an average increase in global mean surface temperature for the final two decades of this century of 3.2-5.4°C relative to the second half of the nineteenth century.  This is a huge change and will be even larger in high latitudes and over continents.  The scale of change is broadly comparable to that which separates our present climate from that of the Ice Age.

I don’t think we have any clear idea of what the full economic, social and political impact of such huge changes would be.  I am all in favour of policies that lift people out of poverty, insecurity and hunger now.  But that does not mean we should ignore the huge risks we are taking with the climate to which humans have become adapted. Presenting this as a sharp dichotomy is wrong.

 

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