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Assessing the Physical Science of Climate Change: IPCC Working Group 1 (2007) From Material Presented by Susan Solomon, co-chair WG I at the Royal Society London, March, 2007 and Norwegian Academy Of Sciences Oslo, Norway April 2007 1. Introduction and Background 2. IPCC Process 3. Key Findings INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) Working Group I The World Has Warmed Globally averaged, the planet is about 0.75°C warmer than it was in 1860, based upon dozens of high-quality long records using thermometers worldwide, including land and ocean. Eleven of the last 12 years are among 12 warmest since 1850 in the global average. IPCC - WGI Intergovernmental Panel on Climate Change Governments require information on climate change for negotiations The IPCC formed in 1988 under auspices of the United Nations Function is to provide assessments of the science of climate change Scientific community contributes widely and on a voluntary basis 75% of the authors in WG1 IPCC (2007) did not work on WG1 IPCC (2001) Substance of IPCC WG1 report in the hands of scientists IPCC - WGI Preparation and Review of the WG1 AR4 • Each report is an assessment of the state of understanding based upon peerreviewed published work. IPCC assesses published research but does not do research. Each assessment goes through multiple reviews and revision and rereview over a period of years. • Informal draft prepared, comments sought from 6-12 outside experts for each chapter (Oct 2004 - Mar 2005). • Formal first order draft (FOD) reviewed by about 600 reviewers worldwide (Sept -Nov 2005). • Formal second order draft (SOD) re-reviewed by about 600 experts worldwide and by dozens of governments (April-May 2006). • Govt comments on revised Summary for Policy Makers (Oct-Nov 2006). • WG1 received and considered over 30000 comments in total. • The assessment conclusions are not the views of any single scientist, but reflect a much broader process. IPCC - WGI The Working Group I Report • • • • • • Started 2004 Completed February 2007 152 Authors ~450 contributors ~600 expert reviewers 30,000+ review comments Contents • Summary for Policymakers You can get it at: • Technical Summary http://ipcc-wg1.ucar.edu/ • 11 Chapters Includes supplementary material. • Frequently Asked Questions All figures available in PowerPoint format. • ~5000 literature references • ~1000 pages IPCC - WGI Industrial revolution and the atmosphere The current concentrations of key greenhouse gases, and their rates of change, are unprecedented. Carbon dioxide Methane IPCC - WGI Nitrous Oxide (ppmv) 350 Last Interglacial Last Ice Age Carbon Dioxide 300 250 200 [Adapted from Figure 6.3, ©IPCC 2007: WG1-AR4] 600 500 400 300 200 100 0 Thousands of Years Before Present Humans are ‘forcing’ the system in a new way. CO2 increases are mainly due to fossil fuel burning. CO2 has not been this high in more than half a million years. IPCC - WGI Ice ages are not random. They are 'forced' (by earth’s orbital clock…. changes in the sunlight received). Better and longer satellite data about the Sun Improved assessment: a) no observed trend in solar irradiance since 1978 using high quality inter-calibrated data; b) spectral information c) solar magnetic flux model rather than proxy data; d) re-evaluation of variations in Sun-like stars. No observed trend in this data. Solar forcing much less than greenhouse gases. IPCC - WGI Human and Natural Drivers of Climate Change Carbon dioxide is causing the bulk of the forcing. On average, it lives more than a hundred years in the atmosphere and therefore affects climate over long time scales. IPCC - WGI Water Vapor Feedback Water vapor responds to changes in climate, but it doesn’t drive changes in climate. It’s a major feedback that amplifies global climate change. New in IPCC (2007): Observed trends that demonstrate the trend, in both the upper troposphere and at the surface. IPCC - WGI Explosive Volcanic Eruptions: Proof of Fast-Response Climate Change Due to Forcing Changing forcing changes the temperature (and water vapor, etc.). If volcanoes can cool, then GHG must warm…. IPCC - WGI Ice Age Forcing and Response Last interglacial [After Figure 6.3, ©IPCC 2007: WG1-AR4] Last Ice age Warming is Unequivocal Rising atmospheric temperature Rising sea level Reductions in NH snow cover And oceans.. And upper atmosphere…. IPCC - WGI Paleoclimate: New and Independent Evidence From Many Types of Past Data eg., changes in glaciers, indicating a global average temperature change in the 20th century consistent with the thermometers. And the corals. And the tree rings. And the boreholes. And the ice cores. IPCC - WGI A different world in the Arctic: present and future The Arctic was also warm in the period 1925-1940, but the extent of warmth was not global at that time. Large future changes in Arctic sea ice are very likely. Changes in sea ice don’t significantly affect sea level because this ice is already floating. Changes in land ice (glaciers, ice caps, and ice sheets) do affect sea level. IPCC - WGI Clear decreases in Arctic sea ice extent. Global distribution of temperature change for June/July/Aug since 1880 http://www.ncdc.noaa.gov/gcag/gcag.html • There are some exceptions to the general trends (land use?), and local ups and downs in individual years • Global warming more likely than not contributed to the 2003 European heat wave. Future? IPCC - WGI Land Precipitation is changing significantly over broad areas Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability. IPCC - WGI A World of Drought Many dry areas are getting drier as soils dry out. Observed sea surface temperature (SST) and links to the pattern of rain in Africa? SSTs and Sahelian rainfall have varied in the past. Some studies suggest links now to the widespread ocean SST trends and global warming. IPCC - WGI Sahelian rainfall decline is reproduced in many models Attribution • Asks whether observed changes are consistent with expected responses to forcings inconsistent with alternative explanations Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely (>90% certainty) due to the observed increase in anthropogenic greenhouse gas concentrations Anthro+ Nat forcing TS-23 IPCC - WGI Understanding and Attributing Climate Change Anthropogenic warming is likely discernible on all inhabited continents Observed Expected for all forcings Natural forcing only IPCC - WGI Solar Attribution studies • Separate time-space patterns of response. • Solar response has very different behavior to GHG, especially with altitude. The upper atmosphere would be expected to be much warmer than it is if solar irradiance were the cause of current surface climate change. IPCC - WGI “All” forcings Changing winds, temperatures and storm tracks • Anthropogenic forcing has likely contributed to circulation changes (storm tracks, winds and temperature patterns) • Warmer, wetter winters in Norway; drier in Spain (and North Africa) IPCC - WGI What’s in the pipeline and what could come Warming will increase if GHG increase. If GHG were kept fixed at current levels, a committed 0.6°C of further warming would be expected by 2100. More warming would accompany more emission. CO2 Eq 3.4oC = 6.1oF 850 2.8oC = 5.0oF 600 1.8oC = 3.2oF 0.6oC = 1.0oF IPCC - WGI 400 A1B is a typical “business as usual” (2090-2099) scenario: Global mean warming 2.8oC; Much of land area warms by ~3.5oC Arctic warms by ~7oC; would be less for less emission IPCC - WGI Projections of Future Changes in Climate New in AR4: Drying in much of the subtropics, more rain in higher latitudes, continuing the broad pattern of rainfall changes already observed. IPCC - WGI What else happens in a hotter world? Observations of sea level rise from satellites, 1993-2003. The global average SLR for the 20th century was about 6 inches (0.17m), mostly from expansion of the hot ocean, and with contributions from glacier melt (Alaska, Patagonia, Europe….). Future changes just from these processes could be up to 1.5 feet (0.5 m) by 2100, and up to 3 feet (1 meter) within about 2-3 centuries, depending on how much GHGs are emitted. But what about other processes? Rapid ice flow? IPCC - WGI Ice shelves influence glacier flow The break up of the Larsen B ice shelf off the Antarctic Peninsula in February 2002 is illustrative of the speed up of glaciers after the blocking of the ice shelf is removed. Glaciers lost ice shelf and sped up Other examples, such as Jakobshavn Glacier (Greenland), show speed up in flow after collapse of the floating Glacier still has ice shelf and did glacier tongue. not speed up IPCC - WGI [Image courtesy of http://nsidc.org/iceshelves/larsenb2002/] Sea level rise and the ice sheets 7m of SL equivalent is on Greenland. This is expected to melt slowly, and raise sea level on a time scale of millennia, for warming >2-5°C. BUT rapid ice flow has been observed - and is not in current models. Could sea level rise be much faster than thought? Some glaciological studies suggest this is transient and will stop. Others suggest it may increase. Future? IPCC - WGI Past Change in The Greenland Ice Sheet The last time polar regions were significantly warmer (by 3-5°C) than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise. White and black dots show drill sites where ice older than 125,000 years is and is not found. IPCC - WGI The IPCC Sequence of Key Findings…… IPCC (1990) Broad overview of climate change science, discussion of uncertainties and evidence for warming. IPCC (1995) “The balance of evidence suggests a discernible human influence on global climate.” IPCC (2001) “Most of the warming of the past 50 years is likely (>66%) to be attributable to human activities.” IPCC (2007) “Warming is unequivocal, and most of the warming of the past 50 years is very likely (90%) due to increases in greenhouse gases.” IPCC - WGI And More…. • Forcing: Greenhouse gases are at unprecedented levels, and are forcing the climate to change. • Beyond global warming: Discernible human influences on other aspects of climate including heat waves, wind patterns, drought, and more…this is the first ‘earth system’ IPCC report. • Commitment: Already committed to more warming (next few decades), with choices about emissions affecting the longer term more and more. • Expected future earth system changes: likely to virtually certain: more extremes, wet in some places, dry in others, etc... • Long term: Sea level rise is inexorable and will continue, and the face of the planet will change. By how much? How fast? IPCC - WGI IPCC - WGI