Global warming could make Spring arrive even earlier than scientists have predicted.
In warmer weather, plants produce their first leaves and flower earlier in the year. In order to predict the effect global warming may have on this, plant scientists have carried out experiments in which they warm a small area over several years and record the advance in flowering and leafing dates.
"We use small-scale warming experiments to predict future changes," lead author Dr. Elizabeth Wolkovich says. "We wanted to look at this assumption we have that these experiments will give us similar answers to long-term records."
But by analysing the results of many of these experiments alongside data from long-term observational studies, in a study called a meta-analysis, scientists from the National Centre for Ecological Analysis and Synthesis have shown that this could significantly underestimate the effect. Long-term observational studies report the advance in flowering and leafing to be up to eight fold larger than warming experiments have demonstrated.
"If we look at long-term records, we see that for every degree celsius of warming, we find five to six days' advance in plant leafing and flowering. For the experiments, it's something like half a day to one-and-a-half days at most," Dr. Wolkovich explains.
As plants form the basis of many ecosystems and food webs, the date at which they produce leaves and flowers has a huge impact upon the local ecology. In addition, flowering and leafing dates affect the uptake of carbon dioxide by plants, as well as the nitrogen cycle and even the water supply. The problem is that for much of the world, we lack long-term records and so are completely reliant on predictions made from these warming experiments - and this could be leading us to dramatically under-predict the future effects of climate change.
There is some good news, too. Dr. Wolkovich believes that warming experiments currently underway are better designed, and can give a more accurate picture of the effects of global warming. More and more studies are also looking at other factors associated with global warming - such as changes in rainfall. But it's important that we carry on with the long-term studies alongside this.
"I think we really need to go after what caused this discrepancy. It could be that short-term experiments are only going to get us part of the way towards what we're seeing in the long term, and something else is going on in the long-term data," Dr. Wolkovich cautions.