Image caption "Warming chambers" are used to assess how plants respond to elevated temperatures

Scientific models are failing to accurately predict the impact of global warming on plants, says a new report.

Researchers found in long-term studies that some are flowering up to eight times faster than models anticipate.

The authors say that poor study design and a lack of investment in experiments partly account for the difference.

They suggest that spring flowering and leafing will continue to advance at the rate of 5 to 6 days per year for every degree celsius of warming.

The results are published in the journal Nature .

For more than 20 years, scientists have been carrying out experiments to mimic the impacts of rising temperatures on the first leafing and flowering of plant species around the world.

The bottom line is that the impacts might be bigger than we have believed until now This Rutishauser, Oeschger Centre for Climate Change Research

Researchers had assumed that plants would respond in essentially the same way to experimental warming with lamps and open top chambers as they would to changes in temperatures in the real world.

Very little has been done to test the assumption until this study lead by Dr Elizabeth Wolkovich, who is now at the University of British Columbia in Vancouver.

With her colleagues she studied the timing of the flowering and leafing of plants in observational studies and warming experiments spanning four continents and 1,634 plant species.

According to Dr Wolkovich, the results were a surprise.

"What we found is that the experiments don't line up with the long term data, and in fact they greatly underestimate how much plants change their leafing and flowering with warming," she said.

"So for models based on experimental data, then we would expect that plants are leafing four times faster and flowering eight times faster in the long term historical record than what we're using in some of the models."

'Consistent message'

Observational data have been gathered by scientific bodies for many years. In the UK, the systematic recording of flowering times dates back to 1875, when the Royal Meteorological Society established a national network of observers.

Since then, data has also been recorded by full-time biologists and part-time enthusiasts, and in recent years there have been mass-participation projects such as BBC Springwatch.

This new research suggests that these observations of flowering and leafing carried out in many different parts of the world over the past thirty years are remarkably similar according to Dr Wolkovich.

"In terms of long term observations, the records are very coherent and very consistent and they suggest for every degree celsius of warming we get we are going to get a five- to six-day change in how plants leaf and flower."

She argues that the difficulties in mimicking the impacts of nature in an artificial setting are much greater than many scientists estimate. The team found that in some cases the use of warming chambers to artificially raise temperatures can sometimes have the opposite effect.

Image caption National and international citizen scientist efforts will help provide much more data to resolve the question

"In the real world, we don't just see changes in temperature - we see changes in precipitation and cloud patterns and other factors - so certainly when you think about replicating changes in clouds, we are very, very far away from being able to do that.

"I guess we will never get to perfectly match nature, but I am hopeful as scientists we can do much, much better, given funding resources."

The team found that the greater investment in the design and monitoring of experiments, the more accurate the result.

"We have a very consistent message from the long-term historical records about how plants are changing, but we need to think more critically about how we fund and invest in and really design experiments," said Dr Wolkovich.

"We do need them in the future, they are the best way going forward to project how species are changing but right now what we're doing isn't working as well as I think it could."

Other researchers were equally surprised by the results.

Dr This Rutishauser is at the Oeschger Centre for Climate Change Research at the University of Bern in Switzerland. He says that in light of this work scientists will have to rethink the impacts of global warming.

"The bottom line is that the impacts might be bigger than we have believed until now. That's going to provoke a lot of work to probably revise modelling results for estimations of what's going to happen in the future for food production especially."

Dr Wolkovich agrees that if the models are so significantly underestimating the real world observations, there could be also be impacts on water the world over.

"If a whole plant community starts growing a week earlier than we expect according to these experiments, it's going to take up a lot more water over the growing season and if you add to that many years of the model projections, you are going to see big changes in the water supply."

She appeals to people to get involved in citizen science projects and help gather data on flowering and leafing, especially in remote areas.

The National Phenology Network in the US logged its millionth observation this week, and similar programmes are underway in the UK , Sweden , Switzerland , and the Netherlands , and a pan-European database is under development.

"We have very few monitoring networks. We need many, many people out there observing this because it is changing faster and across more habitats than we are currently measuring - we need more help!"