Chapter 4 reviews observational data on glacier melting, sea ice area, variation in precipitation, and sea level rise. We find no evidence of trends that could be attributed to the supposedly anthropogenic global warming of the twentieth century.

Chapter 4 Key Findings

• Glaciers around the world are continuously advancing and retreating, with a general pattern of retreat since the end of the Little Ice Age. There is no evidence of a increased rate of melting overall since CO2 levels rose above their pre-industrial levels, suggesting CO2 is not responsible for glaciers melting.

• Sea ice area and extent have continued to increase around Antarctica over the past few decades. Evidence shows that much of the reported thinning of Arctic sea ice that occurred in the 1990s was a natural consequence of changes in ice dynamics caused by an atmospheric regime shift, of which there have been several in decades past and will likely be several in the decades to come, totally irrespective of past or future changes in the air’s CO2 content. The Arctic appears to have recovered from its 2007 decline.

• Global studies of precipitation trends show no net increase and no consistent trend with CO2, contradicting climate model predictions that warming should cause increased precipitation. Research on Africa, the Arctic, Asia, Europe, and North and South America all find no evidence of a significant impact on precipitation that could be attributed to anthropogenic global warming.

• The cumulative discharge of the world’s rivers remained statistically unchanged between 1951 and 2000, a finding that contradicts computer forecasts that a warmer world would cause large changes in global streamflow characteristics. Droughts and floods have been found to be less frequent and severe during the Current Warm Period than during past periods when temperatures were even higher than they are today.

• The results of several research studies argue strongly against claims that CO2-induced global warming would cause catastrophic disintegration of the Greenland and Antarctic Ice Sheets. In fact, in the case of Antarctica, they suggest just the opposite-i.e., that CO2-induced global warming would tend to buffer the world against such an outcome.

• The mean rate of global sea level rise has not accelerated over the recent past. The determinants of sea level are poorly understood due to considerable uncertainty associated with a number of basic parameters that are related to the water balance of the world’s oceans and the meltwater contribution of Greenland and Antarctica. Until these uncertainties are satisfactorily resolved, we cannot be confident that short-lived changes in global temperature produce corresponding changes in sea level.

Chapter 4. Observations: Glaciers, Sea Ice, Precipitation, and Sea Level (PDF, 598 kb)

     4.1. Glaciers (PDF, 214 kb)
            4.1.1. Global
            4.1.2. Africa
            4.1.3. Antarctic
            4.1.4. Arctic
            4.1.5. Europe
            4.1.6. North America
            4.1.7. South America

     4.2. Sea Ice (PDF, 98 kb)
            4.2.1. Antarctic
            4.2.2. Arctic

     4.3. Precipitation Trends (PDF, 125 kb)
            4.3.1. Global
            4.3.2. Africa
            4.3.3. Arctic
            4.3.4. Asia
            4.3.5. Europe
            4.3.6. United States
            4.3.7. Canada and Mexico

     4.4. Streamflow (PDF, 127 kb)
            4.4.1. Eurasia
            4.4.2. North America

     4.5. Sea-level Rise (PDF, 196 kb)
            4.5.1. Mean Global Sea Levels
            4.5.2. Antarctica Contribution to Sea Level
            4.5.3. West Antarctic Ice Sheet
            4.5.4. Greenland Ice Cap