1. How has the climate changed during the recent past? 2. What can we say about current climate change? 3. How do climate models work and what are their predictions for the future? What we wish to learn Today:

Possible Causes of Climate Change Power: 4 x W 2 x W Long-Term 1.Solar Luminosity 2.Shifting Continents 3.Greenhouse gases Medium-Term 1.Orbital parameters 2.Greenhouse gases Short-Term 1.Oceans 2.Sunspots 3.Volcanoes 4.Greenhouse gases

Causes of Climate change A. Tectonic C. Oceans / GHGB. Orbital D. ??

Recent Trends in Temperature Departures in temp (deg C) from mean Global Temperature Data from thermometers Year

Solar Activity and Climate Maunder Minimum: Very few sunspots were seen between 1645 and 1715 Corresponds to the time of the “Little Ace Age” Sunspot number Little Ice Age

BUT, Change in sunspot number is greater than change in solar radiation. The change in solar radiation is only about 0.1%, too small to account for the full temperature shifts – an ongoing investigation… Sunspots and measured solar radiation

Pre-1991 Post-1991 VOLCANO ! Ash on cars

Volcanic eruptions cool global temperature Volcanoes spew out ~160x less CO 2 than humans do…

Satellite troposphere temperature data El Niño index El Niño effect on temperature Satellite data minus El Niño effect Volcano effect on temperature After removing El Niño and volcanoes Residual Trend: 0.11°C per decade Effects of El Niño and volcanoes on air temperatures Pinatubo ’97-98 El Niño

Summary of Climate Forcings in “energy” terms of Watts per m 2 Orbital variations ~ 0.5 W m -2 / century (occurs over long time scales) Solar variation ~ 0.29 W m -2 peak-to-peak over ~2 centuries Greenhouse Gases - past: ~ W m -2 / century CO 2, 4050 BC to ~1000 AD ~ W m -2 / century CH 4, 4050 BC to ~ 1500 AD ~ W m -2 / century N 2 O, 4050 BC to ~ 1000 BC Volcanic eruptions 0 down to -10 W m -2, but short lived (a few years). Estimated long-term mean forcing ~ -0.3 W m -2 * Current GHG emission – Doubling of CO 2 ~ 4 W m -2 !

Past and Modern Changes on Earth CO 2 CH 4 Temp.

Global distribution of CO 2, N. Hemisphere S. Hemisphere

Global distribution of CH 4,

Atmospheric CO 2 concentration and temperature are correlated in the Vostok ice core Temperature variations (ºC) Atmospheric CO 2 concentration (ppm) Glaciations Deglaciations Modern

Paleoclimate provides perspective on where we are headed … IPCC Projections to N.H. Temperature (°C) Global Temperature (°C)

Types of Models: Physical Models (a desktop globe) Statistical Models (a regression, y=mx+b) Conceptual Models (a flow chart) Computer Models (Global Climate Models, GCMs) “Climate models are only sophisticated tools, not crystal balls” “A useful model is not the one which is true, but the one that is informative” “ …all models are wrong, some are useful” USING MODELS TO PREDICT CLIMATE

What goes into a climate model?

“Climate change” is not just an environmental issue… INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC)

The models must use “scenarios” of future GHG emissions World CO 2 emissions Gigatons of Carbon There are many different “storylines”

Pick your future… Source: IPCC TAR 2001

Climate models work pretty well… Rainfall [annual] Which is observed and which is modeled ?

… but there is some variation Prediction of the El Nino by 6 different GCM models

Models show that anthropogenic causes of temperature change explain what has already occurred. Courtesy W. Washington/NCAR

Predictions of large climate changes even by the 2050s Hadley Centre for Climate Prediction and Research

But, we control our destiny -- Temperature from the present day to the 2080s Hadley Centre for Climate Prediction and Research c Unmitigated Emissions c c Stabilization of CO 2 at 550 ppm Stabilization of CO 2 at 750 ppm

Take Home Message: Prediction is Difficult, Especially into the future…

Summary 1.Recent changes in Earth's paleoclimate record are likely due to shifts in ocean circulation, and the effects of greenhouse gas increases. Volcanoes have had only a small effect, and the sun spot record cannot account for the heat input needed. 2.Temperature changes and greenhouse gas abundances are correlated. Rapid global warming is underway and models have been developed to predict the effects of these changes. 3.Global Climate Models (GCMs) predict a much altered climate on Earth during the next century.