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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
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.
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
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."
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.
"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
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. Such projects
are underway in the US and 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!"