Source of much of the information and graphics for this presentationIntergovernmental Panel on Climate Change (IPCC)Birthed by United Nations

Mandate to synthesize scientific consensus on climate change and its impacts

First Report 1995: Global synthesis of climate data & models and projections of impactsSecond Report 1998: Regional analyses of climate trends, future climate scenarios, and impact scenarios for natural and human systemsThird Report 2001: 3 Working groups, 23 disciplines, 1200 scientists. Much more actual observations of changes in climate and in impacts. Improved climate projections. Improved attributionFourth Report in progress - due out 2007

IPCC 1995 (First Assessment Report) Global warming has occured, and it may be due to anthropogenic greenhouse gas emissions

IPCC 1998 (Second Assessment Report) concluded that: The balance of evidence suggests a discernable human influence on global climate.

IPCC 2001 (Third Assessment Report) concluded that Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.Research from the climate science community over the past decade has strengthened the causal links between observed changes in Earths climate system and human activities

Observed Changes in Earths climate

Greenhouse gases = gases that absorb and emit infrared radiation (heat). Presence of greenhouse gases in lower atmosphere traps heat & raises global temperature. Durations up to 100 years. Main ones:

Water vaporCarbon dioxide (industry, cars, wood fires)Nitrous oxide (fertilizing & tilling land, industry, cars)Methane (wetlands, rice paddies, cows)Ozone (air pollution)

Indicators of the Human Influence on the Atmosphere during the Industrial Era

Global average temperatures are increasing with increases in CO2.

The Relative Influences of Different forcing Factors on Global Temperatures

Models show warming of 1930s/40s was due to natural factors (the sun, fig a), but warming of last 30 years was due to humans (fig b)

The relationship between temperature and carbon dioxide over the past 160,000 years.Clear correlation between atmospheric CO2 and temperature over last 750,000 years (not all shown)

Current level of CO2 is outside bounds of natural variability

Rate of change of CO2 is also unprecedentedSource: OSTPCurrent 380 ppm

Climate Change Attribution:How do climate scientist know that current warming is caused by humans? Fingerprint in climate data Fingerprint in ocean temperatures & processes Fingerprint in ocean circulation changes Model simulations

Percent of the Continental U.S. with A Much Above Normal Proportion of Total Annual Precipitation From 1-day Extreme Events (more than 2 inches or 50.8mm)Source: Karl, et.al. 1996.

Observed changes in Earths climate since 1860

Increased global mean temperature, and more heat wavesSea level has risen by several inchesIncreased global cloudinessWarming mainly at night and during winterIncreased global rain and snowfall, and more very heavy rain and snow days (floods and winter storms)More frequent and more intense El Nio yearsMore severe hurricanes in the AtlanticLarge declines in most temperate and tropical glaciers (30% - 60% volume loss)Large decline in Arctic sea ice, freshening of Arctic & N Atlantic oceans, slowing of North Atlantic conveyor belt All are statistically significant changes All have been causally linked to human activities (primarily burning of oil, coal & gas). This is called attribution

Climate models

Global Climate Models Global Climate Model: GCM Atmosphere-ocean general circulation models AOGCM (coupled ocean and atmosphere models) Regional Models - higher resolution than GCMs

Other termsEnsemble = often means many simulations done w/same model & same forcing, but different initial conditionsOr, can mean taking the mean (average) of many different model outputs

1-3 = diff realizations of CCCma CGCM1 model4 = ensemble mean of the 4 outputs with different initial conditions done with same model

Why do climate projections differ?Different resolution: 1.5 - 5 LL, 1 latitude ~ 100 km. (affects ability to model small scale weather & climate events, like thunderstorms)Different sensitivities (how much warming occurs for given change in a radiative forcing, like a doubling of CO2)Different parameterizations (estimations) of processes they dont have direct data for (e.g. clouds)Differences in what processes are coupled into model (Oceans? Land use change?)Different emissions scenarios

Greenhouse Gas Emission ScenariosA1 = techno-world: rapid economic growth & techno-growth, but remains heavily dependent on fossil fuels. Different A1 scenarios are for diff techno developmentA2 = business as usualB1 = Green global: economies shift towards less materialism and techno-fix of more renewables. Economies still run globally (as now)B2 = Green local: strong emphasis on local economies and sustainable development, with moderate techno and economic growth

Change in gas concentration under different scenarios

Ensemble of scenarios

ensemble temperature projections (all models used, take the mean)Top fig: A2 bottom fig: B2 scenarios

Ensemble precipitation projections, A2 (be as usual)& B2 (green local) scenarios

GCMs scales of 5x5 Lat/long (500 km2) to 2.5x2.5 (250 km2). Hadley is now going to 1.5 in new model theoretically can do 50km, but not practical many models, each good/bad at something sensitivity = how much warming does model give for fixed forcing once reaches equilibrium (usu 2xCO2) w/o ocean, system stabilizes in 10s yrs w/ocean coupled, takes 1000s yrs

Differences among models in projected average global temperature increase for a given emission scenario

From IPCC 2001

Level of agreement among modelsLevel of agreement among models for projected temperatures

Level of agreement among models for projected temperatures

Level of agreement among models for projections of precipitation

Averages vs IndividualityProblem - majority rulesCan show each model, but still ask about level of model agreement - so maj still rulesExceptions or extremes may be most likelyExceptions or extremes may be unlikely but high impact (e.g. shutdown of N. Atlantic circulation)Solution - show ensembles, but also show extremes

Rahmstorf, S. 2002. Nature 419:207Ocean currents also distribute heat around globeOcean Circulation Systems. Driven by winds, thermohaline circulation (salty cold water drops down, fresh warm water floats up), and tides

Rahmstorf, S. 2002. Nature 419:207Low probability, high impact extreme event:The Day After Tomorrow scenario Shutdown of North Atlantic Deep Water Circulation - figure shows changes in surface air temperature if conveyor belt in Atlantic shuts down

Global temperature over the past 65 million years.PRESENT1,000 ya13 mya65 mya

Impacts Resulting from Projected Changes in Extreme Climate Events

Projected Changes during the 21st Century in Extreme Climate Phenomena and their Likelihooda

Representative Examples of Projected Impactsb

(all high confidence of occurrence in some areasc)

Simple Extremes

Higher maximum temperatures, more hot days and heat wavesd over nearly all land areas (Very likelya)

Increased incidence of death and serious illness in older age groups and urban poor [4.7]

Increased heat stress in livestock and wildlife [4.2 and 4.3]

Shift in tourist destinations [Table TS-2 and 5.7]

Increased risk of damage to a number of crops [4.2]

Increased electric cooling demand and reduced energy supply reliability [Table TS-4 and 4.5]

Higher [Increasing] minimum temperatures, fewer cold days, frost days and cold wavesd over nearly all land areas (Very likelya)

Decreased cold-related human morbidity and mortality [4.7]

Decreased risk of damage to a number of crops, and increased risk to others [4.2]

Extended range and activity of some pest and disease vectors [4.2 and 4.3]

Reduced heating energy demand [4.5]

More intense precipitation events (Very likelya, over many areas)

Increased flood, landslide, avalanche, and mudslide damage [4.5]

Increased soil erosion [5.2.4]

Increased flood runoff could increase recharge of some floodplain aquifers [4.1]

Increased pressure on government and private flood insurance systems and disaster relief [Table TS-4 and 4.6]

Impacts Resulting from Projected Changes in Extreme Climate Events

Complex Extremes

Increased summer drying over most mid-latitude continental interiors and associated risk of drought (Likelya)

Decreased crop yields [4.2]

Increased damage to building foundations caused by ground shrinkage [Table TS-4]

Decreased water resource quantity and quality [4.1 and 4.5]

Increased risk of forest fire [5.4.2]

Increase in tropical cyclone peak wind intensities, mean and peak precipitation intensities (Likelya, over some areas)e

Increased risks to human life, risk of infectious disease epidemics and many other risks[4.7]

Increased coastal erosion and damage to coastal buildings and infrastructure [4.5 and 7.2.4]

Increased damage to coastal ecosystems such as coral reefs and mangroves [4.4]

Intensified droughts and floods associated with El Nio events in many different regions (Likelya)

[See also under droughts and intense precipitation events]

Decreased agricultural and rangeland productivity in drought- and flood-prone regions [4.3]

Decreased hydro-power potential in drought-prone regions [5.1.1 and Figure TS-7]

Increased Asian summer monsoon precipitation variability (Likelya)

Increase in flood and drought magnitude and damages in temperate and tropical Asia [5.2.4]

Increased intensity of mid-latitude storms (Little agreement between current models)d

Increased risks to human life and health [4.7]

Increased property and infrastructure losses [Table TS-4]

Increased damage to coastal ecosystems [4.4]

Global Average Temperature Is Increasing

The term global warming is used to describe the enhanced greenhouse effect resulting from human activities. The blue line shows CO2 records from ice cores, the tan line shows CO2 records from atmospheric measurements in Hawaii, and the red line shows mean yearly temperature trends.This steady increase of CO2 in the atmosphere has caused greater retention of heat and a gradual warming of the earth: global average surface temperature has risen by about 1F over the last century. Temperature Trends in the U.S.Data from climate stations across the U.S.A. show that most regions of the country have warmed over the past 100 years. Trend analysis shows that temperatures have warmed between 1.8 and 5.4F (13C) over much of the U.S. A. Rainfall patterns have also changed across the U.S.A. Over, there has been an increase in precipitation events (rain and snow), and precipitation is coming down in fewer, more extreme events (floods and very heavy snowfalls).(Reno Gazette) Gary Barbato of the National Weather Service. During 2003, average temperatures for the months of January, June and July (USA?) were all the hottest since records began in 1888, with September 2003 and September 2001 tied for the warmest average.The relationship between temperature and carbon dioxide over the past 160,000 years.

CO2 is higher now than it has been in the past 160,000 years

Ice core samples show that there has been a very clear correlation between atmospheric CO2 concentrations (blue line) and the global temperature record (yellow line). In other words, on a millennial time scale, fluctuations of CO2 and temperature have roughly mirrored each other over the last 160,000 years. One can also see from this graph that the earth has, in the past, experienced some pretty major fluctuations in temperature and CO2 concentration. These fluctuations are between glacial and interglacial cycles.

Ice core studies reading back as far as 420,000 years ago yield the same results. Before human activities, CO2 fluctuated between 180 and 280 ppm (as in this graph) - this is an indication of natural variability. Note that changes in CO2 have been strongly correlated with changes in temperature during this very long time period.

Significant points about the current situation: At 360 ppm, the current level of atmospheric CO2 is already far higher than it has been at any point during the past 420,000 years. Current CO2 levels are outside the bounds of natural variabilityThe rate of change in CO2 concentration is also unprecedented - its increasing faster now than in the past 420,000 years.Shows lag time of climate stabilizing when have model with oceans being coupled to the atmosphere. Pretends that co2 suddenly doubles all in one go, and then just stays there (no additional increase). New temperature stabilized in a few centuries, but sea level rise takes thousands of years to stabilizeThese different scenarios of how greenhouse gase will increase in future are based on different stories of how society and technology will change. These 4 are the major ones that GCMs have used to come up with projections. This is one source of differences among model outputs.Results of different emission scenarios showing how much scenarios differ in how different gasses increase over time.- broken down by type of greenhouse gas(warming agent)The lines represent ensemble means of many different models put together. Output is in terms of watts/m-sq, energy added, which is closely related to temperature.4 boxes are top left - winter season under A2 scenario; top right winter season under B2; bottom left summer season under A2; bottom rt summer season under B2.grey color means models disagree not just on extent of change in precip, but on sign - e.g some models say will be wetter, some drierNote - there is much more disagreement among models in precip than in temp projectionsGlobal temperature over the last 65 million years.

People commonly believe that the current increases in temperature and CO2 are not really unusual, because geologists and paleoclimatologists can point to time periods in Earths past that were even more extreme than what we see today. How unusual are the recent climate changes? One way of asking that is to ask how far back in time we have to go before we come upon changes as great as what the earth is experiencing today.

Todays temperatures are hotter than they have been in the past 10,000 years. Further, climate has been relatively stable over this time period, but is suddenly changing more rapidly than it has in the past 10,000 years.

Going back further we reach the Pleistocene period, during which the earth cycled between glacial (frozen) and interglacial (warm) periods. Todays temperatures are at or beyond the peak high temperatures of the warmest interglacial periods. If we go all the way back to 13 million years ago, we start to see occasional periods in which temperature and CO2 levels were as high as they are today, but these were relatively brief.So when was the last time the climate of the earth was clearly more extreme than todays? If we go all the way back to the age of the dinosaurs, 65-100 million years ago, we finally come to a time when CO2 was really much higher than it is today. The climate was also very different - it was much warmer and wetter.So, yes, Earth has experienced climate much hotter than todays, but human civilization has not.