Do you feel that birds and fish are good indicators of global warming?

Global Change Signs

As the astronauts looked down from the shuttle during their recent flight, they were able to see signs of widespread environmental destruction on Earth. The Great Wall of China is by no means the only sign of mankind that can be seen from space. Commander Eileen Collins said that they could see erosion and deforestation. She was not the first to express concern about the environment. Back in 2001 then commander of the International Space Station (ISS) Frank Culbertson said that astronauts had seen signs of climate change. From their vantage point they can see dust storms, storms, droughts, hurricanes, changes in land use, fires to clear land, deforestation, smoke and dust. They also see how well lit-up the Earth is at night by our lights.

Fortunately we don't have to wait for a shuttle flight or take a trip to the ISS to observe the Earth from above. NASA's Earth Observatory publishes new images each day and there's an archive. It not only shows weather, earth and see temperatures and vegetations, but how the glaciers are retreating. NASA's Astronomy Picture of the Day also includes some pictures of the Earth, including one showing the Earth at Night, all lit up.

Another way of observing climate change is phenology, the study of natural seasonal or cyclic events. Put simply, by observing the signs of spring to see if it is coming earlier, and the signs of autumn (fall) to see if it comes later, we can tell if the average temperature is rising over time. Maps of the extent of glaciers also give an indication, as do marks showing historical sea levels.

As well as the arrival and departure times of birds and fish, and the timing of the seasons of native plants, their ranges may change in reaction to the temperature as well as to other factors such as human disturbance. When the other known factors are allowed for, there remain quite a few changes which would appear to be due to global warming. This includes birds which overwinter in an area where they have only been summer visitors before, or being seen breeding at a higher altitude than before, but not individuals that have been blown astray by a freak storm or hitched a lift. Fish too, have changed their ranges, possibly because the phytoplankton have.

One obvious way of looking for signs of global warming is to record temperature over time. The first temperatures were taken when Galileo Galilei invented the thermometer in 1597. The scientist Robert Hooke made a series of daily measurements from 1664. The oldest set of continuous measurements were begun in 1815 at the Radcliffe Observatory, Oxford. Some measurements have been affected by the fact that a big city grew up around them, and cities tend to be warmer than the surrounding countryside, so even a steady increase may not be an indicator of global warming. An average over the whole Earth is really required, and the trends need to be confirmed by other methods.

As well as the melting of existing glaciers, we can tell something about how the climate used to be by signs of previous glaciers - u-shaped valleys, deposits of morraine and rearrangement of rocks. Another way of looking at the distant past is through fossils - the kind of animals and plants found in an area will depend on what the climate was like. As well as fossils, ancient pollen has a story to tell. Drilling deep cores and looking at the material in each layer allows scientists to go back in time, as much as 140,000 years (at Grand Pile, France). When going a long way back, account has to be taken of the fact that the Earth's land masses have not stood still, but moved around.

So, we have a variety of ways of estimating the Earth's temperature. Some are less accurate but more long term, giving us a feeling for when there were ice ages and when we've been in interglacial periods. Others, more recent, include accurate measurements on the Earth's surface and from space, and corroborating information from phenology. Of course, nothing is simple. For example, global warming could lead to Britain freezing, thanks to the Ocean Conveyor Belt, which goes to show that some phenomena can buck the trend. Also global dimming may have masked the underlying global warming. But as more and more evidence points in the same direction, it is getting harder not to believe in global warming.

Wildlife moves to stay cool in a warmer world

A lot of animals have been noticed in areas further north than they normally go. These include salmon, locusts, warblers, toucans, John Dory fish, bears and butterflies. New species seen by the Inuit in their area include robins, hornets and barn owls. Not everyone believes that this is due to global warming, however, and a few sightings do have other explanations. The study of natural seasonal or cyclic events such as the arrival of birds and flowers is called phenology.

The head of the U.S. Science and Environmental Policy Project, Fred Singer, said, "If you want to measure temperatures, you use a thermometer, not a bird. Birds have all sorts of reasons for moving north, south, sideways or whatever."

Does it matter? In some cases it might. If warblers head north to Canada, then spruce budworm caterpillars may have free rein to attack spruce forests, which could lead to forests becoming more vulnerable to fire.

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