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I've Heard
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I've heard satellite data contradict other evidence of global warming.Until recently, conflicting studies suggested that temperatures measured by satellites revealed a slight cooling trend, whereas the surface temperature record showed a warming trend. This confounded the global warming issue.
Satellites began measurements in 1979 and the surface temperature record, which reveals global warming of about 1.1°F, dates back to about 1860. Satellites take temperatures through vertical slices of the atmosphere, not at the surface. Satellite measurements are also known to be influenced by ozone layer depletion, which has caused cooling of the upper atmosphere. For these and other reasons, satellite and surface data are not expected to be a perfect match. Nevertheless, the discrepancy between the two data sets was too large to be ignored.
Then scientists discovered they neglected some measurement and calibration problems with the satellites, including the fact that satellites were falling from their orbits, which produced an artificial cooling trend. Correcting the satellite data for these problems reveals a small warming trend. These corrections – though not the last word on the satellite vs. surface discrepancy – bring the satellite record into better agreement with surface measurements. Any remaining discrepancies do not invalidate the fact that surface temperatures are rising.
I've heard more CO2 in the air could be beneficial for plants and crops.The impacts of climate change on crops and vegetation depend on complex interactions among increased CO2, rising temperatures, and water and nutrient availability. Elevated levels of CO2 can essentially fertilize plants and crops. However, plant growth is also affected by other factors in addition to CO2 – factors that will be influenced by climate change.
Modest temperature increases, for example, can enhance growth, but if temperatures increase too much growth actually declines. Rising temperatures also increase the process by which plants release CO2. Higher temperatures can increase the rate of evaporation, drying out soils. Insufficient water decreases plant growth. Plants also cannot respond to more CO2 unless sufficient nutrients are available. Furthermore, the growth-enhancing effects of CO2 may diminish over time. Real-world crop yields would also be subject to the hazards of droughts and floods under a changing climate.
I've heard CO2 emissions from human activities are small compared to what's released by nature.The Earth has a natural CO2 cycle that moves massive amounts of CO2 into and out of the atmosphere. The oceans and land vegetation release and absorb over 200 billion metric tons of carbon into and out of the atmosphere each year. When the cycle is balanced, atmospheric levels of CO2 remain relatively stable.
Human activities are now adding about 7 billion metric tons of carbon into the atmosphere every year, which is only about 3-4% of the amount exchanged naturally. But that's enough to knock the system out of balance, surpassing nature's ability to take our CO2 emissions out of the atmosphere. The oceans and land vegetation are absorbing about half of these emissions; the other half remains airborne for 100 years or longer. This is what is causing the rapid buildup of CO2, a buildup that dwarfs natural fluctuations.
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