Xuebin Zhang1, Francis W. Zwiers2 and Thomas C. Peterson3
The improving understanding of climate change
The Nobel Peace Prize winning Intergovernmental Panel on Climate Change (IPCC) reports that “warming of the climate system is unequivocal” and that “most of the observed increase in global average temperature since the mid-20th century is very likely” human-induced (IPCC, 2007(a)). This assessment is the result of many decades of work by the world scientific community. The IPCC published its First Assessment Report in 1990. It concluded that:
- Human activities had substantially increased the atmospheric concentration of greenhouse gases;
- The amount of global warming was broadly consistent with climate model predictions, but was also of the same magnitude as natural climate variability;
- Unequivocal detection of the enhanced greenhouse effect was not likely for a decade or so.
The Second Assessment Report (IPCC, 1996) concluded that the balance of evidence suggested a discernible human influence on global climate and that the climate was expected to continue to change in the future although there were still many uncertainties.
This was followed by the Third IPCC Assessment Report in 2001, which stated that there was new and stronger evidence that most of the warming observed in the second half of the 20th century was likely due to human activities.
Seventeen years after the release of the First Assessment Report, the IPCC in its Fourth Assessment Report assessed with clarity the role of anthropogenic greenhouse gases in warming the climate system on global and continental scales.
Global warming is now evident, not only in the observations of global average air and ocean temperature increases, but also in the widespread melting of snow and ice, rising global average sea level, and increase in temperature extremes. In addition, human influence on temperature is detected at continental, sub-continental, and even regional scales. Detectable changes associated with warming are also observed in other components of the climate system, such as the global atmospheric circulation (Gillett et al., 2003), the global distribution of precipitation over land (Zhang et al., 2007), humidity (Willett et al., 2007; Santer et al., 2007) and the regional hydrological cycle (Barnett et al., 2008). The evidence also suggests that widespread changes in the temperature and other aspects of the climate system are now affecting many physical and biological systems on all continents (IPCC, 2007(b)).
Despite the very significant advances that have been made, much work remains to be done. It remains necessary to quantify the role of human influence on the climate system on smaller scales and on aspects of the climate system not directly related to warming. In addition, it is becoming increasingly important for the global community to have better information on past, present and future climate in order to adequately adapt to a changing climate.
Mitigation and adaptation
It is increasingly evident that action is required to limit the extent and impacts of human-induced climate change. Mitigation, the reduction of anthropogenic forcing on the climate via the reduction of greenhouse gas emissions to the atmosphere and other means, is essential to reduce, delay or avoid impacts in coming decades. However, the effect of mitigation is not immediate, since the greenhouse gases emitted to the atmosphere in the past will remain in the atmosphere for a long time, resulting in an unavoidable warming over the next 30-40 years and beyond (IPCC, 2007(a)). Thus, irrespective of whatever mitigation might be taken, adaptation to a changing climate will be required—an inevitability that has been termed the “adaptation imperative”.
Adaptation will not alter the course of climate change, but it is required to minimize its adverse impacts. For example, railroad tracks can buckle during extremely hot weather. However, steps can be taken when laying railroad track that can raise the threshold temperature at which they buckle (Peterson et al., 2008). If undertaken, this would be an example of adaptation to anticipated climate change. Some planned adaptation to climate change is already occurring on a limited basis. For example, the design of the 13-km long Confederation Bridge, which was opened in 1997 and connects Prince Edward Island to the Canadian mainland, takes into account the possibility of a 1-m sea-level rise due to climate change. Nevertheless, much more extensive adaptation than is currently occurring is required to reduce vulnerability to climate change (IPCC, 2007(b)).
A key question decision-makers ask before commencing an adaptation measure is what climate should they adapt to? There is, unfortunately, no easy answer to this question as there are still uncertainties and many unknowns related to changes in the climate and climate extremes that are highly relevant to the impacts of climate change and, therefore, to adaptation. This includes critical limitations in our ability to monitor climate change globally and regionally, i.e. to observe the climate and to document the changes that have already taken place and are currently taking place.
Impacts resulting from climate change occur typically on regional or local scales and very often result from extremes in weather and climate. For example, the 2006 drought in China was the worst in over 50 years, affecting tens of millions of people. The deadly 2003 European heat wave resulted in many deaths related to the heat and air pollution, including more than 14 800 deaths in France alone (Pirard et al., 2005). The summer of 2007 was the wettest ever observed in the United Kingdom with floods causing widespread damage. With increasing global temperature, changes in regional and local weather and climate extremes that cause adverse impacts will occur more frequently. Effective adaptation to changing weather and extremes requires not only more and better information about future changes in climate from improved climate models, it also requires better monitoring of current climate and more information about past climate change.
Projected waiting times (left) for late 20th-century 20-year return values of annual maximum 24-hour precipitation rates in the mid-21st century by 14 global climate models that contributed to the IPCC Fourth Assessment Report, for different regions (right) as defined under different emission scenarios (adapted from Kharin et al., 2007). Three global domains (GLB: the entire globe; LND: global land areas; and OCN: global ocean areas) are also considered.
The projected changes in waiting time are summarized in a “box and whiskers” display for each region. Each box and whisker display consists of a coloured box with lines (whiskers) extending above and below the box. The vertical extent of the whiskers in both directions describes the range of changes projected by all 14 climate models used in the study. The boxes indicate the central 50 per cent of model projected changes, and the horizontal bar in the middle of the box indicates the median projection amongst the 14 models (seven models project waiting times longer than the median and seven models project waiting times shorter than the median). Although the uncertainty range of the projected change in extreme precipitation is large, almost all models suggest that the waiting time for a late 20th century 20-year extreme 24-hour precipitation event will be reduced to substantially less than 20 years by mid-21st century, indicating an increase in the extreme precipitation at continental and sub-continental scales under all three forcing scenarios.
Armed with such information, engineers who design projects to construct stormwater-handling systems and other types of hydrological infrastructure would be able to include adaptation in their project recommendations. Such recommendations would presumably strike a balance between possible increases in risks from more frequent extremes, and the additional costs that are associated with building structures capable of dealing with larger water quantities than would be suggested by extreme value analyses based only on currently available climate and hydrological data. The overall risk involved in such an adaptation is relatively modest, particularly if the incremental cost of accommodating increased risks from projected climate change is small: should the risk of extremes not increase (which seems unlikely given current projections (IPCC, 2007)) the infrastructure will simply offer more protection against present day extremes and be more durable than anticipated since it will experience extremes that exceed its design capacity less frequently than anticipated.
Adaptation needs reliable climate change information
Unfortunately, climate science does not yet provide all the information needed for adaptation. Our understanding of climate change on the scales at which we can adapt is perhaps not much better than our understanding of global climate change at the time of the IPCC First Assessment Report (IPCC, 1990). What seems certain about is that human activities have changed the global climate, that climate change will continue and that the related changes at regional and local level will cause adverse impacts. Extremes can have positive or negative effects. On balance, however, because systems have adapted to their historical range of extremes, the majority of the impacts of events outside this range are expected to be negative.
Several factors have contributed to the large uncertainties in our understanding of past and current changes in regional and local climate. It is evident from the Fourth Assessment Report (IPCC, 2007(a)) that there is need to improve climate models, particularly on regional and local scales. However, a great deal of fundamental work is also required to increase our ability to document and monitor current and past climate change in order to bridge the gap between the information needed for effective adaptation and the available science. For example, a projection of an increase in the future risk of a certain type of extreme event, such as the 20-year 24-hour rainfall event (Kharin et al., 2007; see box opposite) becomes more useful when designing new infrastructure if we are also able to confidently estimate the size of such an event in the current climate.
Continuing scientific research and climate monitoring is critical for better understanding the causes of current climate change and its impacts, and for providing the information needed to inform adaptation decisions. As is apparent from the IPCC’s ability to assess climate change and its impacts in different parts of the world (see for example, Christensen et al., 2007), the science is advanced most effectively for the benefit of all users when knowledge and information are exchanged internationally and openly. This requires enhanced climate monitoring, renewed resolve to exchange current and historic weather and atmospheric composition data internationally under WMO Resolution 40, and also the training of a new generation of climate scientists around the world especially in developing countries and Least Developed Countries. Enhanced monitoring and research will bring us a better understanding of past and current climate change and its causes, better climate predictions and reduced uncertainties in projected climate change.
The continued accumulation of basic climate data is vital to the understanding of past and current climate change, to improving projections that are well constrained by past observed changes and to developing adaptation strategies that, first and foremost, ensure that new infrastructure and systems are well adapted to current climate change. Climate monitoring, as prescribed in the Second Report on the Adequacy of the Global Observing Systems for Climate in Support of the United Nations Framework Convention on Climate Change (WMO/TD No. 1143) of the Global Climate Observing System, is therefore absolutely necessary. It provides important intelligence as we navigate in the more uncertain world of climate change in near-real-time and attempt to adapt to those changes effectively and in the most cost-effective manner.
Yet, in many places around the world, current climate monitoring networks are inadequate to document regional and local climate change. Moreover, monitoring networks in many parts of the world have been deteriorating since the 1990s. Given the looming adaptation imperative, it is urgent that this decline be reversed. Moreover, in some countries basic climate archives of such important variables such as daily precipitation and temperature are highly vulnerable to permanent loss and damage because they are still in paper form. In addition, even where digitized, archives have not always been properly quality controlled and organized. These fundamental problems, together with restricted access, have prevented the data from being used in climate analysis to the benefit of all. Experience shows that investments in the digitization, quality control and open dissemination of climate data inevitably increase the value and utility of climate data. It is an almost impossible task to develop an effective adaptation strategy if one does not know the past climate sufficiently well since the past serves as the baseline of comparison for projected climate changes.
Climate change detection and indices workshops
An Expert Team on Climate Change Detection and Indices (ETCCDI) workshop involves participants from neighbouring countries and several well-qualified experts from around the world to provide guidance on the analysis of climate data. ETCCDI provides software for the data analysis. Computers for the participants were also provided by sponsoring agencies for some workshops. A workshop typically starts with each participant presenting information on the climate of their country as well as their daily precipitation and temperature data. The participants then learn data quality control and homogenization procedures, and conduct the computation and analysis of climate indices. At the end, the participants give a brief presentation on their national results, and an expert collates the results and gives an overview of the trends and variability in extremes across the whole region. The benefits of working across national borders become obvious when similar results from neighbouring countries verify the analyses. The workshops are enhancing the capacity of countries to extract important climate change information from their long-term daily data, as well as fostering regional collaboration in climate analyses.
Adaptation needs local expertise, regional climate information, and open exchange of knowledge and data
Adaptation is implemented at regional and local levels by stakeholders who often do not have training in climate science. Climate, climate change, and vulnerabilities to climate change differ from one region to another, and thus it is obvious that regionally and locally specific climate change information is required for adaptation. Adaptation is also a slow process, involving considerable outreach and education to ensure that climate and climate change information is included in the adaptation decision-making processes. With the advancement in climate science, and increasing human influence on climate, regular evaluation of regional and local climate change should provide better insight into the regional climate and as a result, less uncertainty for future projections, making adaptation measures more effective. NMHSs should therefore be an integral part of informed decision-making in the adaptation processes for their respective countries, since they are best placed to provide the knowledge about past and current climate variability and change in their regions. Experience throughout the world shows that NMHSs benefit enormously in this task when data, information and expertise are exchanged openly.
Adaptation to climate change is crucial in all parts of the world but especially in developing countries and Least Developed Countries that often lack the capacity to handle adaptation along with multiple related stresses. This occurs, in part, because they do not have adequate climate monitoring and research capacity. Building scientific capacity in developing countries is therefore a key to successful adaptation to climate change. Capacity building should necessarily include the training of local experts as well as science and technology transfer, such as the provision of necessary research tools. WMO Regional Climate Centres can play a role in transferring science and technology such that necessary expertise can be provided locally.
WMO and its Members have played a major role in advancing the understanding of climate change and adaptation through several internationally coordinated programmes that link research, monitoring, prediction, applications and capacity building to user needs. The WMO/ICSU/IOC sponsored World Climate Research Programme, the World Weather Research Programme, the Global Climate Observing System, the Global Atmosphere Watch atmospheric chemistry programme and the World Climate Programme support the generation of scientific information for the IPCC and other strongly related scientific assessments as well as delivery of applications to users.
The Expert Team on Climate Change and Detection and Indices (ETCCDI) is one example of the many collaborative efforts undertaken between these programmes that involves volunteer scientists from NMHSs and partners. ETCCDI has contributed significantly to the improved understanding of changes in climate extremes (Alexander et al., 2006). The ETCCDI has been able to organize workshops (see box on previous page) on climate extreme indices in many different parts of the world. These and other WMO capacity-building programmes should continue to be supported and enhanced as it is urgent to deliver climate science to every corner of the world.
The release of the IPCC Fourth Assessment Report, which attributes observed global warming to anthropogenic influence with greater certainty than ever before, makes it clear that adaptation to the changing climate will be unavoidable. The adaptation imperative, the looming need to make decisions on future infrastructure and systems that take into account for the effects of the changing climate, will lead to an even greater need to sustain and enhance climate monitoring and science than in the past. There are still large uncertainties and many gaps in our understanding of climate change, particularly at adaptation-relevant regional and local scales, where climate science does not currently meet many adaptation needs. Renewed efforts that are needed in climate science include maintaining and improving climate monitoring systems; a renewed resolve to exchange climate data and information internationally; and continued capacity building in the climate research community in all nations to develop and communicate the relevant climate science to stakeholders and decision makers.
Alexander, L.V., X. Zhang, T.C. Peterson, J. Caesar, B. Gleason, A.M.G. Klein Tank, M. Haylock, D. Collins, B. Trewin, F. Rahimzaden, A. Tagipour, K. Rupa Kumar, J. Revadekar, G. Griffiths, L. Vincent, D.B. Stephenson, J. Burn, E. Aguilar, M. Nrunet, M. Taylor, M. New, P. Zhai, M. Rusticucci, J.L. Vazquez-Aguirre, 2006: Global observed changes in daily climate extremes of temperature and precipitation. J.G.R.—Atmosphere, doi: 10.1029/2005JD006290.
Barnett, T.P., D.W. Pierce, H.G. Hidalgo, C. Bonfils, B.D. Santer, T. Das, G. Bala, A.W. Wood, T. Nozawa, A.A. Mirin, D.R. Cayan, M.D. Dettinger, 2008: Human-induced changes in the hydrology of the Western United States, Science, doi:10.1126/
Gillett, N.P., F.W. Zwiers, A.J. Weaver, P.A. Stott, 2003: Detection of human influence on sea-level pressure. Nature, doi:10.1038/nature01487.
Christensen, J.H., B. Hewitson, A. Busuioc, A. Chen, X. Gao, I. Held, R. Jones, R.K. Kolli, W.-T. Kwon, R. Laprise, V. Magaña Rueda, L. Mearns, C.G. Menéndez, J. Räisänen, A. Rinke, A. Sarr and P. Whetton, 2007: Regional Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
IPCC, 1990: Scientific Assessment of Climate Change—Report of Working Group I (J.T. Houghton, G.J. Jenkins, J.J. Ephraums (eds)). Cambridge University Press, Cambridge, UK, 365 pp.
IPCC, 1996: Climate Change 1995: The Science of Climate Change. Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change. (J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskett (eds)). Cambridge University Press, Cambridge, UK, 572 pp.
IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson (eds)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 944 pp.
IPCC, 2007(a): Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
IPCC, 2007(b): Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (eds)), Cambridge University Press, Cambridge, UK.
Kharin V.V., F.W. Zwiers, X. Zhang and G.C. Hegerl, 2007: Changes in temperature and precipitation extremes in the IPCC ensemble of global coupled model simulations. J. Climate, 20, 1419-1444.
Peterson, T. C., M. McGuirk, T. G. Houston, A. H. Horvitz and M. F. Wehner, 2008: Climate Variability and Change with Implications for Transportation, National Research Council, in press.
Pirard, P., S. Vandentorren, M. Pascal, K. Laaidi, A. Le Tetre, S. Cassadou and M. Ledrans, 2005: Summary of the mortality impact assessment of the 2003 heat wave in France. Euro Surveill, 10, 153-6.
Santer, B.D. et al., 2007: Identification of human-induced changes in atmospheric moisture content. Proceedings of the National Academy of Science, 104, 15248-15253.
Stott, P.A., D.A. Stone and M.R. Allen, 2004: Human contribution to the European heatwave of 2003. Nature, doi:10.1038/nature02089
Willett, K.M., N.P. Gillett, P.D. Jones and P.W. Throne, 2007: Attribution of observed surface humidity changes to human influence. Nature, doi:10.1038/nature06207.
Zhang, X., F.W. Zwiers and P. Stott, 2006: Multi-model multi-signal climate change detection at regional scale. J. Climate, 19, 4294-4307.
Zhang, X., F.W. Zwiers, G.C. Hegerl, F.H. Lambert, N.P. Gillett, S. Solomon and T. Nozawa, 2007: Detection of human influence on twentieth-century precipitation trends. Nature, doi:10.1038/nature06025.
1.Research Scientist, Climate Research Division, Environment Canada, Toronto, Ontario, Canada, Xuebin.Zhang@ec.gc.ca, Member of the Joint CCl/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices
2.Director, Climate Research Division, Environment Canada, Toronto, Ontario, Canada, Francis.Zwiers@ec.gc.ca, co-Chair of the Joint CCl/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices
3.Research Meteorologist, NOAA’s National Climate Data Center, Asheville, North Carolina, United States, Thomas.C.Peterson@noaa.gov, Chair of the CCl Open Area Program Group on Monitoring and Analysis of Climate Variability and Change