Climate Change

Climate Concepts

Climate is what we expect, weather is what we get. Mark Twain

Climate refers to the average weather conditions in a certain place over many years. For example, the climate in Minnesota is cold and snowy in the winter, and the climate in Honolulu, Hawaii, is warm and humid all year long. The climate in one area, like the Midwest or Hawaii, is called a regional climate. The average climate around the world is called global climate.
When scientists talk about global climate change, they're talking about the global climate and a pattern of change that's happening over many years. One of the most important trends that scientists look at is the average temperature of the Earth, which has been increasing for many years. This is called global warming.
Rising global temperatures lead to other changes around the world, such as stronger hurricanes, melting glaciers, and the loss of wildlife habitats. That's because the Earth's air, water, and land are all related to one another and to the climate. This means a change in one place can lead to other changes somewhere else. For example, when air temperatures rise, the oceans absorb more heat from the atmosphere and become warmer. Warmer oceans, in turn, can cause stronger storms.
This diagram shows how the Earth's atmosphere, climate, oceans, snow and ice, and ecosystems are all connected, which means extra greenhouse gases in the atmosphere lead to many other changes.
This diagram shows how global warming can lead to a variety of other changes.

The Earth's Climate in the Past

The Earth was formed about 4.5 billion years ago—that's a very long time ago! It's hard to say exactly what the Earth's daily weather was like in any particular place on any particular day thousands or millions of years ago. But we know a lot about what the Earth'sclimate was like way back then because of clues that remain in rocks, ice, trees, corals, and fossils.
These clues tell us that the Earth's climate has changed many times before. There have been times when most of the planet was covered in ice, and there have also been much warmer periods. Over at least the last 650,000 years, temperatures and carbon dioxide levels in the atmosphere have increased and decreased in a cyclical pattern. Can you see this pattern in the graph below?
These two graphs show how the amount of carbon dioxide and the Earth's temperature have changed over the last 650,000 years. Both graphs show a similar up-and-down pattern.
These graphs are based on the Vostok ice core from Antarctica. They do not include the most recent increases in carbon dioxide and temperature caused by humans. Notice the strong connection between carbon dioxide and temperature. Source: EPA's Climate Change Indicators (2010) and Petit et al. (2001).
People didn't cause the climate change that occurred thousands or millions of years ago, so it must have happened for other natural reasons.

Greenhouse Gases

Greenhouse gases trap heat in the atmosphere, which makes the Earth warmer. People are adding several types of greenhouse gases to the atmosphere, and each gas's effect on climate change depends on three main factors:
Carbon dioxide is the most important greenhouse gas emitted by humans, but several other gases contribute to climate change, too.Learn more about the major greenhouse gases by selecting pieces of the pie chart below.

Greenhouse gases come from all sorts of everyday activities, such as using electricity, heating our homes, and driving around town. The graph to the right shows which activities produce the most greenhouse gases in the United States.
These greenhouse gases don't just stay in one place after they're added to the atmosphere. As air moves around the world, greenhouse gases become globally mixed, which means the concentration of a greenhouse gas like carbon dioxide is roughly the same no matter where you measure it. Even though some countries produce more greenhouse gases than others, emissions from every country contribute to the problem. That's one reason why climate change requires global action. The graph below shows how the world's total greenhouse gas emissions are continuing to increase every year.


The Signs of Climate Change

The average temperature of the Earth is rising, but that's not the only way we can tell the climate is changing. In fact, the signs are all around us! Observations and measurements from all over the world provide strong evidence that the climate has already started to change.

Climate Change's Effects On Temperate Rain Forests Surprisingly Complex

Jan. 18, 2013 — Longer, warmer growing seasons associated with a changing climate are altering growing conditions in temperate rain forests, but not all plant species will be negatively affected, according to research conducted by the U.S. Forest Service's Pacific Northwest Research Station.

Research featured in the January 2013 issue of Science Findings -- a monthly publication of the station -- reveals a complex range of forest plant responses to a warming climate.
" Although the overall potential for growth increases as the climate warms, we found that plant species differ in their ability to adapt to these changing conditions," said Tara Barrett, a research forester with the station who led the study.
Barrett and her colleagues explored trends in forest composition in southeastern and south-central Alaska, home to the bulk of the world's temperate rain forests. The researchers found an uptick in growth in higher elevations of the region over the 13-year period, with an almost eight-percent increase in live-tree biomass, a measure of tree growth. Individual species within the rain forest, however, differed -- western redcedar biomass increased by four percent, while shore pine declined by almost five percent.

As forest managers consider climate impacts like these in the management of their forests, scientists, including Barrett and research biologist David L. Peterson, are communicating climate change science within the agency, helping managers -- in Alaska and beyond -- to meet this challenge.

In another research effort, featured in the December 2012 issue of Science Findings, Peterson summarized the scientific basis for climate change adaptation. He and his colleagues across the country have conducted case studies that revealed the critical role of science-management partnerships in adaptation planning and have produced a climate change guidebook and Web portal for climate science information.
" The main objective is to get science in the hands of managers so that they have the basic information, but also have access to the documentation they need to do their jobs," said Peterson.


Milankovitch Cycles

Astronomer Milutin Milankovitch developed the mathematical formulas upon which these orbital variations are based. He hypothesized that when some parts of the cyclic variations are combined and occur at the same time, they are responsible for major changes to the earth's climate (even ice ages). Milankovitch estimated climatic fluctuations over the last 450,000 years and described cold and warm periods. Though he did his work in the first half of the 20th century, Milankovich's results weren't proven until the 1970s.

A 1976 study, published in the journal Science examined deep-sea sediment cores and found that Milankovich's theory corresponded to periods of climate change. Indeed, ice ages had occurred when the earth was going through different stages of orbital variation.


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