Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace. It's becoming clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650,000 years.
We call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. As the Earth spins each day, the new heat swirls with it, picking up moisture over the oceans, rising here, settling there. It's changing the rhythms of climate that all living things have come to rely upon.
What will we do to slow this warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the face of the Earth as we know it—coasts, forests, farms and snow-capped mountains—hangs in the balance.
The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjfpUwcIdfE-Qq5IThDCegpQ5nJukKVsDsT95k976_1ehg91FyIPr23LuAm35e87f_t4dbfn7YdRV5KxBWlOx3O1HAtqwpTyTt5XdttRBcZMNefRKOt8mWzB25YQWvadobdz-7OBoRVyxK1/s200/greenhouse-effect.jpg)
Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit cooler. In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming.
Levels of greenhouse gases (GHGs) have gone up and down over the Earth's history, but they have been fairly constant for the past few thousand years. Global average temperatures have stayed fairly constant over that time as well, until recently. Through the burning of fossil fuels and other GHG emissions, humans are enhancing the greenhouse effect and warming Earth.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhaTYLMcQkxaJ9hcbCTO5a4EwecTxTIWAc2IL2HVt96Td0MgFAV8AugOGH8aS5N_rWBrXIFqjTKrC5vlX4v5cpTDFw1GWhAYrDndU7WxdzQt1yGLZrucYZuFJboPlm_FHaAcs1iMzQUpZ6t/s320/global_warming_cartoon1_256595.jpg)
The average global temperature and concentrations of carbon dioxide (one of the major greenhouse gases) have fluctuated on a cycle of hundreds of thousands of years as the Earth's position relative to the sun has varied. As a result, ice ages have come and gone.
However, for thousands of years now, emissions of GHGs to the atmosphere have been balanced out by GHGs that are naturally absorbed. As a result, GHG concentrations and temperature have been fairly stable. This stability has allowed human civilization to develop within a consistent climate.
Occasionally, other factors briefly influence global temperatures. Volcanic eruptions, for example, emit particles that temporarily cool the Earth's surface. But these have no lasting effect beyond a few years. Other cycles, such as El Niño, also work on fairly short and predictable cycles.
Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the industrial revolution. Changes this large have historically taken thousands of years, but are now happening over the course of decades.
The rapid rise in greenhouse gases is a problem because it is changing the climate faster than some living things may be able to adapt. Also, a new and more unpredictable climate poses unique challenges to all life.
Historically, Earth's climate has regularly shifted back and forth between temperatures like those we see today and temperatures cold enough that large sheets of ice covered much of North America and Europe. The difference between average global temperatures today and during those ice ages is only about 5 degrees Celsius (9 degrees Fahrenheit), and these swings happen slowly, over hundreds of thousands of years.
Now, with concentrations of greenhouse gases rising, Earth's remaining ice sheets (such as Greenland and Antarctica) are starting to melt too. The extra water could potentially raise sea levels significantly.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4FJ4DAZo8DzfvumuJ9TUnRDzKHI4H7bpcCPXjv_nbLjwmlm7SLUunlSfcB3yr9d3ahm0WP2c7ZvQBrSeXKdbOvaw0DsDi_wVfVvTfoB8AsAklKJnhoWpnpsLDlZwLSwOtWi44la-513X8/s400/before-after-global-warming-glacier1.jpg)
Scientists are already seeing some of these changes occurring more quickly than they had expected.According to the Intergovernmental Panel on Climate Change, eleven of the twelve hottest years since thermometer readings became available occurred between 1995 and 2006.
2 comentarii:
The "greenhouse effect" often gets a bad rap because of its association with global warming, but the truth is we couldn't live without it.
Global Warming is false. The earth goes through a natural heating and cooling process every hundreds of years. We are spitting out gases though, true, but My point is Global Warming is false.
Post a Comment