Climate Change & Global Warming: State of the Science overview December 2009 Nathan Magee

Despite initial La Nina and solar cycle minimum, global mean was is 6 th warmest on record through Oct.

Global temperatures have been increasing at a rate of about 0.2°C per decade. Land has warmed more quickly than ocean, but both are warming steadily. The Arctic has warmed much faster than tropics. Systematic Antarctic warming has not been observed.

Land has warmed more quickly than ocean, but both are warming steadily. The Arctic has warmed much faster than tropics. Systematic Antarctic warming has not been observed.

What has caused the observed warming? Greenhouse gases absorb terrestrial IR radiation and slow the escape of energy to space. Otherwise average earth temperature would be 260 K as controlled by our distance from the sun. As expected, high CO 2 concentrations from ice cores are temporally matched to high temperatures during interglacial periods.

Three most important greenhouse gases have increased extremely rapidly over last century; changes nearly entirely anthropogenic Methane and NO 2 increases have slowed; not CO 2 Calculated anomaly in present global energy balance: “Radiative Forcing”

Aerosols are better at blocking SW and are likely masking a significant portion of the positive greenhouse-gas forcing. Long-term increase in solar irradiance is about 5% as large as greenhouse- gas forcing. Most feedback terms not included here.

a) Black: Measured global temperature since 1900 Red: Modeled global temperature using known historic forcings and feedbacks in 20 GCMs (measurement fits in model envelope) b) Blue: GCM-modeled global temperature without greenhouse forcing (measurement diverges from model)

Ozone depletion and greenhouse absorption at low altitude suggests high- altitude cooling Observations confirm this cooling has been ocurring The General Circulation Models are not predicting weather They’ve successfully captured most of the temporal, geographic, and vertical patterns of temperature change already observed Performance over past century gives an idea of uncertainty going forward

How much warming by 2100? Emission Scenarios RedModest regional environmental advances, continued large emissions growth in developing countries GreenModerate global advances in use of non- emitting energy sources Blue: Successful global GHG emission controls Orange: constant CO 2 concentration Bottom Line Best Guess at 2100: +2.8 ° C

The warming will not be distributed evenly in time or space Warming gradually slows with time under more “green” emission scenarios Our emission decisions may not make a big impact in 15 years, but they will be clearly apparent to our children and grandchildren in 85 years.

Extra Slides Below for potential questions

Who is doing climate science? The research itself is being done by scientists and students at Universities across the world (including TCNJ) US and International Government Laboratories Private foundations and corporations The Intergovernmental Panel on Climate Change: 800 scientific authors and 2500 expert science reviewers IPCC Doesn’t sponsor or conduct new climate research but has been organized by the UN and WMO to collect and publish new and consensus science on climate change.

How much warming has ocurred?