Climate Change: The Latest Scientific Assessment Anthony D. Socci, Ph.D. U.S. Environmental Protection Agency Emerging Growth Issues Workshop June 27, 2001

Key Points Is there a greenhouse effect? Yes, the existence of a natural greenhouse effect is well established. Heat-trapping greenhouse gases such as CO 2, CH 4, water vapor and N 2 O prevent a significant portion of incoming solar radiation from escaping back into space resulting in warming at the Earth’s surface. In the absence of these gases, the Earth’s average temperature would be 60 º F (33.4 ° C) cooler. Have greenhouse gases increased as a consequence of human activities? Yes, greenhouse gases such as CO 2, CH 4, and N 2 O have increased considerably since 1750, the start of the industrial revolution. In the case of carbon dioxide and methane, present levels of these gases have not been exceeded in the last 420,000 years. Are we experiencing a global warming? Yes, the global average temperature of the Earth’s surface has warmed by about 1.0 º F (0.6 ° C) since 1860, mostly during the latter half of the 20 th Century. The warming is real and particularly strong within the last 20 years. Is this warming due to the increase in greenhouse gas concentrations? Most of the observed warming over the last 50 years is likely to be due to the increase in greenhouse gas concentrations.

Key Points Continued Are human activities contributing to a global warming? The warming over the past 100 years is very unlikely to be due to internal climate variability alone, and it is unlikely to be entirely natural in origin. Current thinking suggests that human activities are responsible for at least part of the observed warming, especially over the latter half of the 20 th Century. Global warming could well have serious adverse societal and ecological impacts by the end of this century, especially at the upper end of the IPCC temperature projections. Even in the more conservative scenarios, models project temperatures and sea-levels that continue to increase well beyond the end of this century, suggesting that assessments that only examine the next 100 years may well underestimate the magnitude of the eventual impacts. Risk increases with increases in both the rate and the magnitude of climate change. Sources: IPCC WG I Summary for Policy-Makers, Third Assessment Report, 2001; Climate Change Science, National Academy of Sciences, 2001.

Human Influence on the Atmosphere during the Industrial Era Different symbols denote ice core data for several sites in Antarctica and Greenland Source: IPCC WG I (Science) Summary for Policy-Makers, Third Assessment Report, CO 2 up 31% CH 4 up 151% N 2 O up 17%

Temperature and CO 2 concentration over the last 420,000 years. The present atmospheric CO 2 concentration is 367 ppmv (parts per million by volume), the highest level seen in the last 420,000 years. Source: Petit, Jouzel, et al, Nature, 1999.

Observed globally-averaged temperatures, The mean annual temperature has risen by about 0.6 ˚C (1.2 ˚F) since The eight warmest years in this modern instrumental record occurred in the decade of the 1990s and are listed here in descending order , 1997, 1995, 1990, 1999, 2000, 1991 and Source: NOAA National Climate Data Center.

Observed and Reconstructed Surface Temperature Anomalies for the Northern Hemisphere Over the Past 1,000 Years The rate and duration of warming in the 20th century has been much greater than in any of the previous nine centuries. It is likely that the 1990s have been the warmest decade, and 1998 the warmest year of the millenium. The gray region represents the 95% confidence range. Source: IPCC WG I Summary for Policy-Makers, Third Assessment Report, 2001.

Simulated Annual Global Mean Surface Temperatures Source: IPCC WG I (Science) Summary for Policy-Makers, Third Assessment Report, 2001.

The Global Climate of the 21st Century Range of Projected Outcomes from the IPCC Special Report on Emission Scenarios (SRES) 40 Total Scenarios Source: IPCC WG I (Science) Summary for Policy-Makers, Third Assessment Report, 2001.

Variations of the Earth’s Surface Temperature: 1000 to to 1861, N. Hemisphere, proxy data; 1861 to 2000 Global, Instrumental; Gray shaded areas represent 95% confidence range (through 2000) 2000 to 2100, SRES projections Source: IPCC WG I (Science) Summary for Policy-Makers, Third Assessment Report, 2001

Plausible Impacts Higher maximum temperatures and more hot days and heat waves over land areas (VL). Higher minimum temperatures and fewer cold days, frost days and cold waves (VL). More intense precipitation events over many areas (VL). Increased summer drying over most mid-latitude continental interiors and associated risk of drought (L). Intensified droughts and floods associated with El Nino events in many different regions (L). Note: Judgmental estimates - VL = % chance; L = % chance that result is true.

Plausible Impacts for the U.S. Reduced lake levels and outflows for the Great Lakes/St.Lawrence (MC). Enhanced coastal erosion, flooding, loss of wetlands and increased storm surges especially off FL and much of the Atlantic coast (HC). Vector-borne diseases may expand ranges in North America (MC). Exacerbated air quality and heat stress morbidity and mortality may occur (MC). Weather-related insured losses and public sector disaster relief payments in N.America have been increasing - potential for surprises (HC). Note: Judgmental estimates - HC = %; MC = %. Source: IPCC SPM, Third Assessment Report, Climate Change 2001: Impacts, Adaptation and Vulnerability, 2001.

Number of Billion Dollar Weather Disasters Source: NOAA/National Climate Data Center, 2000

Unresolved Issues How much warming will occur? How fast will the planet warm? How much of the warming is natural and how much is human-induced? What are the regional details of how climate change will manifest itself in the future? Other sources of uncertainty: clouds and the role of water vapor in the upper atmosphere, regionally. Models do some things well.

Administration’s Position on Global Climate Change The President takes global climate change very seriously. He is committed to addressing the issue in a manner that protects our environment, consumers and economy. The U.S. opposes the Kyoto Protocol because it exempts many countries from compliance and would cause serious harm to the U.S. economy. The Administration is undertaking a Cabinet-level review of U.S. climate change policy. This review will consider what policies this Administration should pursue domestically and internationally. We are optimistic that, working constructively with our friends and allies through international processes, we can develop technologies, market-based incentives, and other innovative approaches to global climate change.