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12: Climate
12.18: Causes and Effects of Global Warming

12.18: Causes and Effects of Global Warming

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What is the human cost of warmer temperatures?

Many lands are marginal for farming. When rainfall is normal or high, the lands can produce. When rainfall is low, no crops grow. Drought makes marginal lands unsuitable for farming. Drought can also make good lands more difficult to farm. These changes will increase as temperatures warm.

Causes of Global Warming

The average global temperature has been rising since the end of the Pleistocene, with some ups and downs, of course. Rising temperatures are natural for this time period. But natural causes cannot explain all the warming that's been happening. There is some other factor at work.

Recent global warming is due mainly to human actions. The actions involve releasing greenhouse gases into the atmosphere. Remember that greenhouse gases keep the atmosphere warm? And that carbon dioxide is a greenhouse gas? When humans burn fossil fuels, carbon dioxide is released into the atmosphere. The more carbon dioxide in the atmosphere, the better the atmosphere can trap heat. In other words, an increase in greenhouse gases leads to greater greenhouse effect. The result is increased global warming. Pictured below is the increase in carbon dioxide since 1960 (Figure below).

Graph showing increasing carbon dioxide levels over time

How much more carbon dioxide was in the air in 2010 than in 1960?

Burning forests also releases carbon dioxide into the atmosphere. Other human activities release greenhouse gases into the atmosphere. For example, growing rice and raising livestock both produce methane.

Effects of Global Warming

There are already many effects of global warming being seen. As Earth has gotten warmer, sea ice has melted. This has raised the level of water in the oceans about 3 mm per year. The rate of sea level rise is now accelerating and might be more than 10 mm per year in 2100. Although this doesn’t sound like much, added together over the years it can be a lot. The greatest danger from flooding will be when storm surge is added to the top of higher sea levels.

Graph showing the sea level has risen 9 inches since 1870

The overall trend in sea level since 1870; it has risen about 9 inches.

The extent of Arctic sea ice in summer has been decreasing rapidly. The ice pictured below is the sea ice minimum in 2016 (Figure below). The yellow line is the median minimum ice extent for 1981–2010.

Drawing of the Arctic sea ice minimum for 2011

The sea ice minimum for 2016 (pictured) was the third lowest on record, with 2012 as the lowest. 2017 was slightly higher, although records have not been updated.

Other effects of global warming include more extreme weather. Earth now has more severe storms, floods, heat waves, and droughts than it did just a few decades ago. Many living things cannot adjust to the changing climate. Coral reefs in many parts of the world are struggling to survive. Species are moving uphill where temperatures are cooler. Those at the top of the mountain are being run off. Migration and egg-laying behaviors in birds are off of their normal. There are many more examples of the effects of changing climate.

Summary

Greenhouse gases trap heat in the atmosphere. Burning fossil fuels and other human activities release greenhouse gases into the atmosphere.
Greenhouse gas levels in the atmosphere are increasing. Global temperatures are increasing.
Changes due to increasing temperatures are seen around the globe. Living organisms and humans are also affected.

Review

What do you expect to happen if you increase the amount of greenhouse gases in the atmosphere?
What has happened to the level of carbon dioxide in the atmosphere in the past several decades (use numbers and units)?
What has happened to sea level since 1870 (use numbers and units)?
What are some of the effects of climate change that are already being seen?