How do we know global climate change is happening?

by: Clem Guttata

Wed Nov 17, 2010 at 08:25:22 AM EST

The physics and chemisty behind the greenhouse effect is quite simple. We've known about it for well over 100 years (Joseph Fourier proposed it in 1824, Svante Arrhenius followed up with tests in 1896).

Certain types of chemicals, called "greenhouse gases" cause the absorption and emission of infrared radition in the atmosphere to warm the earth's lower atmosphere and surface.

As this diagram shows, greenhouse gas like water vapor, carbon dioxide (CO2), methane (CH4) and ozone (O3) in the atmosphere cause heat to be trapped and returned back to the earth's surface.

Image from Wikimedia

So, how do we know if global climate change is really happening?  

The scientific evidence that our world is warming is unmistakable. More than 300 scientists from 160 research groups in 48 countries contributed to the report, which confirms that the past decade was the warmest on record and that the Earth has been growing warmer over the last 50 years.

Based on comprehensive data from multiple sources, the report defines 10 measurable planet-wide features used to gauge global temperature changes. The relative movement of each of these indicators proves consistent with a warming world. Seven indicators are rising: air temperature over land, sea-surface temperature, air temperature over oceans, sea level, ocean heat, humidity and tropospheric temperature in the "active-weather" layer of the atmosphere closest to the Earth's surface. Three indicators are declining: Arctic sea ice, glaciers and spring snow cover in the Northern hemisphere.

"For the first time, and in a single compelling comparison, the analysis brings together multiple observational records from the top of the atmosphere to the depths of the ocean," said Jane Lubchenco, Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. "The records come from many institutions worldwide. They use data collected from diverse sources, including satellites, weather balloons, weather stations, ships, buoys and field surveys. These independently produced lines of evidence all point to the same conclusion: our planet is warming,"

Image from NOAA

The report emphasizes that human society has developed for thousands of years under one climatic state, and now a new set of climatic conditions are taking shape. These conditions are consistently warmer, and some areas are likely to see more extreme events like severe drought, torrential rain and violent storms.

The evidence is clear. Climate change is here. Today.