TOPICS IN GLOBAL WARMING  
 
Do Climates Change? Is Climate Changing Now? Causes of Change
Is Current Change a Problem? Future Climates What Can Be Done?
     
 
One thing climate scientists today attempt to do is determine, or model, what the climate will be like in the future if current trends continue. This is difficult to do, because many factors contribute to climate and how it changes (see Causes of Change). We don’t fully understand how all of these elements interact with one another, and there may be some we haven’t identified yet. However, we do know that the climate change we are experiencing now cannot be due to natural variation alone. Over the next 1000 years, all the natural causes of climate change combined would likely not produce a temperature increase of 1 degree C; as you will see below, current projections of global warming resulting from human-induced greenhouse gas emissions expect temperature increases between 2 and 8 degrees C.
 
     
   
  Graphs courtesy of Global Warming Art (Click for more information (left); Click for more informaiton (right))  
     
 
These figures show two different ways of predicting global temperature change in the next 100 years. The graph on the left shows eight models of temperature change based on the so-called ‘A2’ emissions scenario. This is a scenario for the future that assumes the world has a large population (~15 billion by 2100) and moderate use of fossil fuels but high total energy use overall. The data for the models is from the International Panel on Climate Change’s Data Distribution Center (IPCC-DDC), and the average temperature in 2000 is taken to be zero for all eight models. The two dark blue models indicate that by 2100, global temperature will have risen by two degrees, while the red model predicts that it could be as much as 5 degrees. The average prediction of these models is that global temperature in 2100 will be 3.5 degrees C higher than it is now.

The image on the right is based on the assumption that economic growth continues at present rates and humans do not take any substantial steps to reduce or counter the effects of greenhouse gas emissions. Future temperature changes will likely not be uniform over the Earth’s surface, and this figure indicates that temperature increases will be greater on land than in the ocean. This makes sense, as water heats and cools much more slowly than either air or land do. The average, or zero-level, temperature in this model is the average global temperature from 1960-1990; the most significant changes are in northern South America and near the North Pole, where temperatures may be as much as 8 degrees C higher in 2100 than they are at present.

Increasing atmospheric CO2 is the primary anthropogenic cause of temperature increase, because of how it influences the greenhouse effect.
 
     
   
  Graphs courtesy of Global Warming Art (Click for more information)  
     
 
This figure, from the National Oceanic and Atmospheric Administration, shows a projection of sea ice thickness in 2050 based on an atmosphere-ocean circulation model, a computerized model for predicting climate change. This model projects that sea ice thickness in the Arctic in 2050 will be approximately half what it was in the 1950s.
 
     
   
  Graphs courtesy of Global Warming Art (Click for more information)  
     
 
This graph shows observed sea level change from 1950 to 2000 based on tide gauge measurements (black line), and seven models for sea level change until 2100 (colored lines). These models assume that economic growth continues at present rates and humans do not take any substantial steps to reduce or counter the effects of greenhouse gas emissions. The average prediction from these models is that sea level will rise 40cm, 15.7 inches, by 2100; the most extreme prediction is that sea level will rise almost 60cm, or 24 inches (2 feet), and the least extreme predicts 20 cm, or 8 inches, of sea level rise.
 
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