Despite a scientific consensus on the subject, some people don't think global warming is happening at all. These groups of scientists think the data doesn’t show a measurable upward trend in global temperatures, either because there isn’t enough long-term historical climate data or because the data isn't clear enough. They also believe that people who are already worried about global warming are interpreting the data incorrectly. That is, these people are looking for evidence of global warming in the statistics, instead of looking at the evidence objectively and trying to figure out what it means. While others argue any increase in global temperatures we are seeing could be a natural climate shift, or it could be due to other factors than greenhouse gases.
But here’s another view of those who have done various studies on the subject and completely believe in it.
Signs that the Earth is warming are recorded all over the globe. The easiest way to see increasing temperatures is through the thermometer records kept over the past century and a half. Around the world, the Earth's average temperature has risen more than 1 degree Fahrenheit (0.8 degrees Celsius) over the last century, and about twice that in parts of the Arctic.
This doesn’t mean that temperatures haven't fluctuated among regions of the globe or between seasons and times of day. But if you average out the temperature all over the world over the course of a year, you see that temperatures have been creeping upward. Although we can't look at thermometers going back thousands of years, we do have some records that help us figure out what temperatures and concentrations were like in the distant past. For example, trees store information about the climate in the place where they live. Each year, trees grow thicker and form new rings. In warmer and wetter years, the rings are thicker. Old trees and wood can tell us about conditions hundreds or even several thousands of years ago.
Key to the past is also buried under lakes and oceans. Pollen, creatures, and particles fall to the bottom of oceans and lakes each year, forming sediments. Sediments preserve all these bits and pieces, which contain a wealth of information about what was in the air and water when they fell. Scientists reveal this record by inserting hollow tubes into the mud to collect sediment layers going back millions of years.
For a direct look at the atmosphere of the past, scientists drill cores through the Earth's polar ice sheets. Tiny bubbles trapped in the gas are actually pieces of the Earth's past atmosphere, frozen in time. That's how we know that the concentrations of greenhouse gases since the industrial revolution are higher than they've been for hundreds of thousands of years.
Computer models help scientists to understand the Earth's climate, or long-term weather patterns. Models also allow scientists to make predictions about the future climate. Basically, models simulate how the atmosphere and oceans absorb energy from the sun and transport it around the globe. Factors that affect the amount of the sun's energy reaching Earth's surface are what drive the climate in these models, as in real life. These include things like greenhouse gases, particles in the atmosphere such as from volcanoes and changes in energy coming from the sun itself.
What's the correct answer? It can be hard to figure out. Most scientists will tell you that global warming is real and that it is likely to do some kind of harm, but the extent of the problem and the danger posed by its effects are always wide open for a good debate.
Photo by Telegraph.