Transcript Slide 1
What we wish to learn Today: 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? Possible Causes of Climate Change Long-Term 1. Solar Luminosity 2. Shifting Continents 3. Greenhouse gases Medium-Term 1. Orbital parameters 2. Greenhouse gases 1. 2. 3. 4. Power: 4 x 1026 W Short-Term Oceans Sunspots Volcanoes Greenhouse gases 2 x 1017 W Causes of Climate change A. Tectonic B. Orbital C. Oceans / GHG D. ?? N.H. Temperature (°C) 2 Recent Trends in Temperature 1 0 -1 Departures in temp (deg C) from 1961-1990 mean 1000 1200 1400 1600 1800 Year 2000 Global Temperature Data from thermometers Year Solar Activity and Climate Sunspot number Little Ice Age Maunder Minimum: Very few sunspots were seen between 1645 and 1715 Corresponds to the time of the “Little Ace 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 Ash on cars Pre-1991 Post-1991 Volcanic eruptions cool global temperature Volcanoes spew out ~160x less CO2 than humans do… Effects of El Niño and volcanoes on air temperatures Satellite troposphere temperature data ’97-98 El Niño El Niño index El Niño effect on temperature Satellite data minus El Niño effect Volcano effect on temperature After removing El Niño and volcanoes Pinatubo Residual Trend: 0.11°C per decade Summary of Climate Forcings in “energy” terms of Watts per m2 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: ~ +0.0067 W m-2 / century CO2, 4050 BC to ~1000 AD ~ +0.0016 W m-2 / century CH4, 4050 BC to ~ 1500 AD ~ +0.0006 W m-2 / century N2O, 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 CO2 ~ 4 W m-2 ! Past and Modern Changes on Earth CO2 Temp. CH4 Global distribution of CO2, 1992-2001 N. Hemisphere S. Hemisphere Global distribution of CH4, 1992-2001 Atmospheric CO2 concentration and temperature are correlated in the Vostok ice core Modern Temperature variations (ºC) 6 Paleoclimate provides perspective on where we are headed … 5 4 Global Temperature (°C) 3 N.H. Temperature (°C) 2 1 1 0.5 0 -0.5 1000 1200 1400 1600 1800 2000 0 IPCC Projections to 2100 USING MODELS TO PREDICT CLIMATE 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” 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 There are many different “storylines” Gigatons of Carbon World CO2 emissions 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 1997-1998 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 c Stabilization of CO2 at 750 ppm c c Unmitigated Emissions Hadley Centre for Climate Prediction and Research Stabilization of CO2 at 550 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.