An illustration of this inertia is the reduction in the number of glaciers in certain areas. There are about a third less glaciers than 135 years ago. This reduction isn't, however, simply the result of global warming but rather because the Earth is still returning to its normal state after the last Ice Age!
Because the climate system is so slow, the climate will continue to warm up even after greenhouse gas emissions are stabilized or reduced. Sea level will also continue to rise for many hundreds of years after CO2 emissions are stabilized.
The slowness also adds to the uncertainties in our knowledge about climate change. Both the degree to which people add to the greenhouse effect and the possible consequences of human actions are difficult to study because it takes so long from when a gas is emitted to when we can measure the changes. When scientists try to predict the future, it takes a long time from when they make the calculations to when they can check to see if they were right.
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1. SLOW RESPONSE: This figure shows what might happen if man-made emissions of CO2 stop growing at some point during the next hundred years, and then start falling. After CO2 emissions are reduced and concentrations in the atmosphere stabilize, surface air temperatures continue to rise slowly for a century or more. Expansion of the ocean due to warmer water continues long after CO2 emissions have been reduced and melting of ice sheets continues to contribute to sea-level rise for many centuries. Source: IPCC (click to enlarge, 48 kB)
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