What was the research about?

W: Prof Schneider, you and three colleagues just published new research in the Proceedings of the National (U.S.) Academy of Sciences. Could you explain what this tells us?
M: Many current investigations into climate change rely on statistical or physical models—and all models rely on assumptions.
    We thought why not ask plants and animals directly if they have felt any climate changes lately? We wanted to find out if nature had more credible answers than models alone the animals and plants in nature can give us independent evidence of human induced global warming.
    So we looked at more than 130 different plant and bird species in the northern hemisphere—mainly in Northern America and Europe—to see how flowering and migration times have changed. And we compared our findings with a state-of-the-art climate model driven by natural forces like volcanic eruptions, human pressures like greenhouse gas emissions and the combination.
    Normally, such model-driven results are compared to temperature measurements such as thermometers, weather balloons, and satellites—all of which have controversies attached as to their reliability. So we just jumped over the controversy by using plants and animals as "surrogate" thermometers to see if a clear signal emerged.
W: And what was the result?
M: First of all, you can today clearly see how much earlier plants flower in spring—in the thirty years from 1970 to 2000, flowering has moved to an earlier moment by almost ten days. The best fit with the species records came from the computer model driven by the combination of natural and human pressures. In fact the strongest single factor is human forces like greenhouse gases and industrial hazes.
    Secondly you can see that this is in accordance with the climate model that we used a standard model on which many climate scientists rely. So the research shows once more that the general results of the model calculations actually are true—we can see the same basic things the model predicts going on in nature.