{"id":406,"date":"2008-02-29T18:23:16","date_gmt":"2008-02-29T23:23:16","guid":{"rendered":"http:\/\/blogs.edf.org\/climate411\/2008\/02\/29\/forcings_and_feedbacks\/"},"modified":"2008-04-22T14:23:51","modified_gmt":"2008-04-22T19:23:51","slug":"forcings_and_feedbacks","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/climate411\/2008\/02\/29\/forcings_and_feedbacks\/","title":{"rendered":"2 Key Climate Terms to Know"},"content":{"rendered":"

Lisa MooreThis post is by Lisa Moore, Ph.D.<\/a>, a scientist in the Climate and Air program at Environmental Defense.<\/i><\/p>\n

Scientists use some technical terms in discussing climate change that can cause confusion. Two that are especially useful to know are "forcing<\/b>" and "feedback<\/b>".<\/p>\n

You’ll hear these terms a lot in discussions of how human activity impacts climate – and especially when the topic turns to the melting Arctic. If you know what they mean, you’ll have a much better understanding of the dynamics behind climate change.<\/p>\n

<\/p>\n

"Forcing" and "feedback" both refer to effects on the Earth’s climate system.<\/b> Climate changes when there’s a change in climate system’s energy balance<\/a> – the amount of energy absorbed from the Sun, versus the amount of energy radiated back into space from Earth’s lower atmosphere and surface. A process that changes this energy balance – and thus the climate – is called a "climate forcing<\/b>".<\/p>\n

Many things can cause climate forcing. Some, like shifts in the Earth’s orbit around the Sun or volcanic eruptions, are natural events. Others, like increased concentrations of greenhouse gases in the atmosphere, are caused by human activities. Climate change caused by human activity is called "anthropogenic forcing<\/b>".<\/p>\n

A climate feedback<\/b> is an indirect (or "secondary") change within the climate system that occurs in response to a forcing. For example, warmer air can hold more water vapor<\/a>, and water vapor can trap more solar energy in the atmosphere, augmenting the warming effect. This is a positive climate feedback<\/b> because the secondary effect is in the same direction as the primary effect – both are warming.<\/p>\n

Another example of a positive climate feedback occurs with sea ice, which is why you hear the term "feedback" in discussions of Arctic warming<\/a>. As temperatures rise, sea ice melts and exposes open water. Water is darker than ice so it reflects less sunlight and absorbs more energy. This augments the warming effect, leading to more sea ice melting, and so on in a loop.<\/p>\n

Climate feedbacks also can be negative, reducing the initial effect rather than augmenting it. For example, increased water vapor in the atmosphere due to warming can lead to more cloud formation. Thick low clouds can block sunlight from reaching the Earth by reflecting it back into space. This creates a cooling effect – a negative climate feedback<\/b>.<\/p>\n

Positive climate feedbacks are dangerous because they can accelerate climate change towards tipping points<\/a><\/b>, critical thresholds at which a small change qualitatively alters the state of some Earth system. For example, the Greenland Ice Sheet<\/a> could start a slow but irreversible meltdown if global temperature rises above a tipping point, which scientists warn could be just 2\u00b0F above today’s temperature.<\/p>\n

Tipping points also can trigger climate feedbacks.<\/b> For example, if the Earth warms enough to melt permafrost (a tipping point for the Arctic region), the melted ground can release greenhouse gases that, in turn, accelerate warming. In fact, studies show that methane emissions are increasing from areas of thawing permafrost in Siberia<\/a>.<\/p>\n

Sound scary? It is. This is why many scientists are pushing hard for legislation to cap greenhouse gas emissions<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

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