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The Earth's climate has changed throughout history. From ice ages where ice covered significant portions of the Earth to ice ages where ice retreated to the poles or melted entirely - the climate has continuously changed.
Since the Industrial Revolution (around 1750), human activities have substantially added to the amount of heat-trapping greenhouse gases in the atmosphere. The burning of fossil fuels and biomass (living matter such as vegetation) has also resulted in emissions of aerosols that absorb and emit heat, and reflect light.
The addition of greenhouse gases and aerosols has changed the composition of the atmosphere. The changes in the atmosphere have likely influenced temperature, precipitation, storms and sea level. However, these features of the climate also vary naturally, so determining what fraction of climate changes are due to natural variability versus human activities is challenging.
The following pages provide a summary of the atmosphere and climate changes observed during the Industrial Era and, where possible, current understanding of why the changes have occurred .
The release of greenhouse gases and aerosols resulting from human activities are changing the amount . of radiation coming into and leaving the atmosphere, likely contributing to changes in climate.
Greenhouse Gases Greenhouse gas concentrations in the atmosphere have historically varied as a result of many natural processes (e.g. volcanic activity, changes in temperature). However, since the Industrial Revolution humans have added a significant amount of greenhouse gases in the atmosphere by burning fossil fuels, cutting down forests and other activities. Because greenhouse gases absorb and emit heat, increasing their concentrations in the atmosphere will tend to have a warming effect. But the rate and amount of temperature increase is not known with absolute certainty.
Temperatures are changing in the lower atmosphere - from the Earth’s surface all the way through the stratosphere (9-14 miles above the Earth’s surface). Scientists are working to document temperature trends and determine their causes.
Sea Level Changes Sea levels are rising worldwide and along much of the U.S. coast. Tide gauge measurements suggest that sea level has risen worldwide approximately 6-8 inches (15-20 cm) during the last century . A significant amount of sea level rise has likely resulted from the observed warming of the atmosphere and the oceans.
People around the world may feel that the climate has been getting steadily warmer and warmer in recent years. Places which used to be abundant in snowfall have frequently experienced snowfree winters. Drought lasts longer in some dry areas. People find that without air conditioners they could hardly work or fall asleep on hotter summer days.
It is apparent that all the changes caused by global warming is related to human’s bad behavior.
Global warming, I think, is not far away from us, it has already changed our lives. The temperature in shanghai for example, is higher in May than average. So we have lost part of the spring.
To stop global warming we should make immediate and continual efforts. I hope the situation will soon change. Global warming catches and holds our concern, for it affects us and will affect our later generations. We cannot wait any longer. Do it. Do it right. Do it right now.