Climate change
Global warming is already happening
and it is not just temperature
Is the change significant? why, yes
We are no longer involved in just a scientific debate over how observations fit theories A little aside The Hockey Stick controversy This is a political and economic fight How: Seeding doubt, obfuscating, distracting attention from the central problem, junk science, silencing critics
Who s winning? Time/ABC/Stanford poll: About 85% of Americans say global warming is happening right But 65% think scientists disagree about global warming wrong And 81% oppose higher taxes on electricity, 68% oppose higher gasoline taxes Perception and reality the first step is admitting you have a problem living on a fault line
Public awareness or lack of it poll taken in Denver after a month of snow and cold weather
Climate system Climate is basically how the Earth s energy is distributed temperature, rain and snow, wind, etc. Climate models attempt to simulate how this energy is distributed.
Climate system
Feedbacks Climate system The complications come from feedbacks, which can be positive and negative. Positive feedbacks reinforce changes and destabilize systems Negative feedbacks diminish changes and stabilize systems
Climate system
Climate system Example of clouds as feedbacks: Warmer climate means (probably) more clouds Clouds both reflect incoming solar radiation (cooling the planet) and trap outgoing infrared (warming the planet). Which is more important? The consensus is that the cooling effect dominates, but the issue is not totally resolved.
Climate system Key feedback: aerosols SO 2 from coal burning The irony is that we are actively removing SO 2 from smokestacks in coal burning (acid rain issue), yet SO 2 may be responsible for keeping the CO 2 warming smaller
But what about that complex climate system? It is a myth that global climate is too complex to be predictable Climate inputs: Incoming solar energy Aerosols and other reflectors Greenhouse gases If we know these, we can reproduce temperature quite well
Predicting global climate Models, simple and complex, agree with our three inputs, we can account for temperature changes of the past 100 years
The 1970-present warming
Compare with 1920 s
And mid century cooling
Predictions for future climate Consensus is that warming will happen about 50% of energy from the sun is expressed as heat, so this is a good bet mean of model predictions is about 4 C to 5 C increase in global temperatures
Warming will be more at higher latitudes Snow and ice albedo effect
More precipitation overall is expected This is because warm air holds more moisture
But droughts are expected to be more common as continents heat up and dry out due to increased evaporation
Sea level will rise due to: 1. Thermal expansion (about 0.5 m by 2100) 2. Land ice melting another 0.5m or more by 2100 Sea level rise will be more in polar regions why?
Sea level is rising and will continue to rise Thermal expansion, and now(?) ice sheet melting The last time the earth was 3-5 C warmer, sea level was 3 m higher and Greenland ice cap was much smaller (140,000 years ago) Sea Level
Observed Sea Ice Decrease
Sea ice thickness is decreasing
Abrupt climate change Ice core records of past climate change tell us that the climate system has thresholds or tipping points. When one of these is crossed, large changes occur in a short period of time Temperature: 10 C to 15 C in fifty years, 5 C in five years Precipitation: double or halve in 1 to 3 years Atmospheric circulation: fundamental shift in 1 year
Abrupt climate change The standard way that large climate changes occur, esp. in the North Atlantic region
Abrupt climate change Changes of 10-15 C in 50 years Rates of change of 1 C per year over 5 years
200 year comparison to GISP2 at end of YD -250!D ice at end of Younger Dryas NorthGRIP and GISP2!D -300 NorthGRIP GISP2-350 -100-50 0 50 100 Years relative to end of Younger Dryas
Where are the thresholds? 1. Sea ice 1979 2003 2. Ocean circulation (heat re-distribution) 3. Atmospheric circulation (heat re-distribution) Others???
Interplay of ocean circulation and arctic/global climate The Arctic helps to control this circulation, and is warmed by it
Model-data mismatch things happen much faster in the real world
Beware the nasty feedbacks In the Arctic, locked up in frozen soils and lakes, is organic material a.k.a. carbon The amount is impressive roughly equal to all fossil fuels Why does it stay there now? its frozen. Will it remain frozen? not likely.
Polar amplification of warming
Warming is happening
Arctic carbon Field studies show that this release may be beginning:
Arctic carbon Atmospheric observations of CH 4 and CO 2 have not seen a big release, yet. Monitoring of carbon fluxes in the Arctic is ongoing, but with not nearly enough sites NOAA flask network
Arctic Carbon Even with aggressive CO 2 mitigation, if Arctic carbon is released, atmospheric CO 2 and CH 4 levels will rise if policies don t have tangible outcomes, it is difficult to maintain them, and very difficult to implement them
Less certain changes More intense storms More hurricanes (big debate here) How plants will respond (carbon - water interactions Regional climate change
Tornadoes no trend(?)
Hurricanes?
Costs are going up but so are people in harms way
Regional climate change
Spatial trends in temperature
Bottom line for climate Temperatures are rising, and will continue to rise Sea level is rising, and will continue to rise Less snow, more rain Continental drying Sea ice is melting and will continue to melt
Options? We can adapt We can mitigate We can geo-engineer the climate What have we done so far???