Tips 4 Teachers


The Intergovernmental Panel on Climate Change (IPCC) released a report in 2007, which included their forecasts of some of the effects of current climatic changes (from the Wiki entry):

Model projections are made based on an analysis of various computer climate models running within different SRES scenarios. As a result, predictions for the 21st century are as shown below.

• Surface air warming in the 21st century:
  • Best estimate for a "low scenario"[6] is 1.8°C with a likely range of 1.1 to 2.9°C (3.2°F with a likely range of 2.0 to 5.2°F)
  • Best estimate for a "high scenario"[7] is 4.0°C with a likely range of 2.4 to 6.4°C (7.2°F with a likely range of 4.3 to 11.5°F)
  • A temperature rise of about 0.1°C per decade would be expected for the next two decades, even if greenhouse gas and aerosol concentrations were kept at year 2000 levels.
  • A temperature rise of about 0.2°C per decade is projected for the next two decades for all SRES scenarios.
  • Confidence in these near-term projections is strengthened because of the agreement between past model projections and actual observed temperature increases.
• Based on multiple models that all exclude ice sheet flow due to a lack of basis in published literature,[8] it is estimated that sea level rise will be:
  • in a low scenario[6] 18 to 38cm (7 to 15 inches)
  • in a high scenario[7] 26 to 59cm (10 to 23 inches)
• It is very likely that there will be an increase in frequency of warm spells, heat waves and events of heavy rainfall.
• It is likely that there will be an increase in areas affected by droughts, intensity of tropical cyclones (which include hurricanes and typhoons) and the occurrence of extreme high tides.
• "Sea ice is projected to shrink in both the Arctic and Antarctic … In some projections, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century."

Scenario-specific projections are based on analysis of multiple runs by multiple climate models, using the various SRES Scenarios. "Low scenario" refers to B1, the most optimistic scenario family. "High scenario" refers to A1FI, the most pessimistic scenario family.


Home-grown scenarios:


Baseline – assuming baseline trends continue

Best-case: 2028 - Greenhouse gas buildup continues, causing global temperatures to rise, perhaps by as much as 2 degrees C. Crop growth booms, allowing higher yields and longer growing seasons over more parts of the world. Ecosystems are put under stress, but either migrate to appropriate climes or adapt; extinctions occur, but there is no long-term impact from the loss of biodiversity. ...

Alarmist: 2028 - Greenhouse gas buildup continues, causing global temperatures to rise 3 to 6 degrees C, higher in some places. Higher temperatures increase the variability of the water cycle, increasing the frequency and severity of both droughts and floods. Much higher temperatures cause a massive glacier melt and an ice-free Arctic (causing the dark ocean water to absorb more light as heat). Thawing organic matter in northern tundras releases more greenhouse gases and increases the rise in temperature. Severe damage occurs to ecosystems in many regions, and some areas collapse entirely. Barring some extraordinary event, an unstoppable vicious circle of climate change has begun, with much greater damage expected over the coming decades.

The "real" baseline trend would lie somewhere between these two.


Alternative futures – assuming something (government policy, consumer or corporate action, etc) changes

2028 - Greenhouse gas levels have stabilized, with CO2 at somewhere around 475 ppm, through a combination of reduced emissions and sequestration. CO2 sequestration and other greenhouse gas control programs have been on a massive and global scale to maintain modern living conditions. Temperatures may continue to rise (perhaps one degree) after stabilization, but are expected to stop rising within the next hundred years.

2028 - Greenhouse gas levels continue to rise, but the rate of increase has fallen and continues to fall steadily. Levels are predicted to stabilize by 2050, with CO2 levels somewhere below 500ppm. Temperatures have risen and are predicted to continue to rise for some time to come, possibly topping out at an increase of 2.5 degrees C. Rising temperatures have altered the weather, causing considerable stress on humans and ecosystems, but there have been few humanitarian and biological crises and no world-wide collapse. Scientists are still very worried that the climate could spiral out of control, but the governments of the world seem to have acted in time to stop a true catastrophe.

2028 - Governments have responded to the climate crisis by both confronting rising greenhouse gases and implementing several forms of geoengineering, artificially increasing the Earth's albedo. As in the previous scenario, greenhouse gas levels continue to rise, but at a reduced rate. However, the temperature has stayed relatively constant since the geoengineering program went into effect. There have been side-effects on the water cycle and weather patterns that have caused a number of problems, both in human and ecological terms. However, the possibility of a vicious circle of increasing temperature and CO2 levels seems to have been deferred, buying time for more fundamental solutions.

2028 - Greenhouse gas levels continue to rise, but there have been fewer effects than the alarmists have expected. The temperature has increased by 1 deg C, and weather patterns are becoming more severe, but the world hasn't ended. However, the Arctic ice sheet has completely disappeared over the past few summers, and the northern permafrost is thawing rapidly, releasing increasing amounts of methane into the atmosphere. Scientists are becoming ever more worried that there is no turning back from the current trends, and world governments are only recently starting to enact any truly effective programs to stop a downward spiral.





These two graphs are from the IPCC 2007 report, depicting their scenarios for climate change.