What is the IPCC? Intergovernmental Panel on Climate Change

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1 IPCC WG1 FAQ

2 What is the IPCC? Intergovernmental Panel on Climate Change The IPCC is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Programme (UNEP). Its constituency is made of : The governments: the IPCC is open to all member countries of WMO and UNEP. Governments participate in plenary Sessions of the IPCC where main decisions about the IPCC work programm are taken and reports are accepted, adopted and approved. They also participate the review of IPCC Reports. The scientists: hundreds of scientists all over the world contribute to the work of the IPCC as authors, contributors and reviewers. Its role is to assess on a comprehensive, objective, open and transparent basis the latest scientific, technical and socio-economic literature produced worldwide relevant to the understanding of the risk of human-induced climate change, its observed and projected impacts and options for adaptation and mitigation.

3 Human Activities vs. Natural Influences

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5 How are Temperatures on Earth Changing? Warming from the 1920s to 1940s = (.35 o C) 1970s to present = (.55 o C) Increased rate of warming over the previous 25 years 11 of 12 warmest years on record in the past 12 years Warming greater over land Warming slightly greater during winter Cooler areas: Northern North Atlantic near southern Greenland

6 How are Temperatures on Earth Changing? Most warming in middle and lower latitudes, particularly tropical oceans Since 1950s, decrease in # of cold days and increase in # of warm days Length of frost-free season increased in most mid- and high-latitude regions of both hemispheres NH earlier start to spring

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8 How is Precipitation Changing? Significantly wetter in eastern North and South America, northern Europe, and northern and central Asia Drier in Sahel, southern Africa, Mediterranean, and southern Asia More precip now falls as rain instead of snow Increases in heavy precip events has occurred even in drier places Increases in both droughts and floods

9 Palmer Drought Severity Index (Measure of soil moisture)

10 How is Precipitation Changing? Soil moisture acts as air conditioner. Wetter areas (eastern NA and SA) show a smaller temperature increase Water vapor has increased globally by 5% over the oceans which has increased precipitation intensity and risk of heavy rain and snow events Therefore, warmer climate increases risk of both drought where it is not raining and floods- where it is raining More rain less snow equals less snow pack which reduces summer water availability when it is most needed.

11 Change in Extreme Events? Since 1950 the number of heat waves has increased In the last 50 years, significant decrease in cold nights In the last 50 years, significant increase in warm nights Since 1970, 75% increase in Category 4 and 5 hurricanes

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13 Amount of Snow and Ice Decreasing? YES. Observations show a globalscale decline of snow and ice over many years, especially since Mountain glaciers are shrinking Snow is retreating earlier in spring Sea ice is shrinking Permafrost reductions are widespread Snow cover has declined by about 2% per decade since 1966 Glacier, ice cap, ice sheet melt to sea level rise is estimated to be mm/yr between 1993 and 2003

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15 Is Sea Level Rising? YES. There is strong evidence that sea level gradually rose in the 20 th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900 Sea level is predicted to rise at an even greater rate in this century 20 th century estimates of 1.7 mm per year

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17 Is the Current Climate Change Historically Unusual? Concentration of CO 2 has reached a record high relative to more than the past 500,000 years and has done so at an exceptionally fast rate Most of the warming in the past 50 years is attributable to human activities CO 2 concentrations are known accurately for the past 650,000 years. During that time, they varied between 180 ppm and 300 ppm. Now CO 2 is 379 ppm which took about 100 years to increase For comparison, it took over 5,000 years for an 80 ppm rise after the last ice age. Higher values than today have only occurred over many millions of years

18 Is the Current Climate Change Historically Unusual? While there are differences between climate reconstructions, all published reconstructions find that temperatures were warm during medieval times, cooled to low values in the 17 th, 18 th, and19th centuries, and warmed rapidly after that The current RATE of global warming is much more rapid and very unusual in the context of past changes Although large climate changes have occurred in the past, there is no evidence that they took place at a faster rate than the present warming If projections of a 5 o C warming in this century are realized, Earth will have experienced the same amount of global warming as it did at the end of the last ice age There is no evidence that this rate is matched to a comparable global temperature increase over the last 50 million years!

19 Are the Increases in Greenhouse Gases Caused by Humans? YES. In fact, the full extent of the increases is not seen because atmospheric concentrations only account for 55% of the human activity The rest is absorbed by plants and the oceans The relative amount of 13 C in air has been declining which means that the added C is from plants and fossil fuels made from prehistoric plants/animals Between 1960 and 1999 CH 4 concentrations grew at a rate of 6 times faster than over any previous 40 year period in the last 2,000 years Between 1960 and 1999, N 2 O concentrations grew at least twice as fast than over any other 40 year period in the previous 2000 years The 38% increase of tropospheric ozone since the pre-industrial era is human-caused. It is very likely that the increase in combined radiative forcing from CO 2, CH4, and N 2 O was at least 6 times faster between 1960 and 1999 than over any 40 year period in the last 2,000 years

20 How Reliable are Climate Models? VERY. Models can reproduce past and present climate Models have consistently provided a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases Despite some uncertainties (clouds, aerosols, etc.) models are unanimous in their predictions of substantial climate warming under greenhouse gas increases

21 How Reliable are Climate Models?

22 Could the Warming be Natural? Very unlikely that the 20 th century warming can be explained by natural causes Climate records indicate that the 2 nd half of the 20 th century was likely the warmest 50- year period in the NH in the last 1,300 years Models fail to reproduce the observed climate when human activities are removed When human activities are added, models accurately reflect past and present climate changes The human influence on climate very likely dominates over all other causes of climate change during the past 50 years

23 Could the Warming be Natural? No.

24 More Extreme Events? YES. Already increase in frequency and intensity of heat waves and heavy precip events Fewer frost days Increased growing season Fewer cold air outbreaks More summer dryness, winter wetness Intense heavy downpours but also longer dry periods Wet areas will get wetter, dry areas drier More runoff means more warm season floods More intense tropical storms, greater wind speeds and rainfall

25 Day After Tomorrow? Not considered likely in the 21 st century However, such changes may be more likely with time if climate change continues unabated Even if the ocean circulation shut down the relative warming from increased greenhouse gases would overwhelm the cooling due to a colder Atlantic Ocean No climate model predicts Day After Tomorrow even under worst-case scenarios

26 What if Greenhouse Gases were Reduced? Some concentrations decline almost immediately while others still increase for centuries Ex. more than 50% of CO 2 is removed by oceans, 20% remains for thousands of years Therefore, CO 2 concentrations will continue to increase in the long term even if they are reduced today Only a complete shut-off of CO 2 emissions would result in a long-term stabilization at a constant level Cutting CO 2 emissions by 50% today will only stabilize the levels for the next 10 years

27 Work Cited IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., 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.