Good news for climate science from the vegetable world: as global temperatures rise, plants in the forests and fields may breathe in more carbon dioxide, and respire a little less.
In the great carbon budget puzzle – where does all that carbon dioxide released from fossil fuels actually go? – this brings the climate modellers a little closer to a more reliable picture of the future.
Nineteen scientists from Australia, the US, the UK, Sri Lanka, Sweden and New Zealand report in the Proceedings of the National Academy of Sciences that they re-examined one of the assumptions in climate modelling. This was that, as temperatures rose, plants would work harder to stay cool – and breathe out, or respire, more carbon dioxide.
Although photosynthetic growth is based on the abstraction of CO2 from the atmosphere, the conversion of the carbon to plant tissue and the release of oxygen for the benefit of the animal world, plants all respire a proportion of that carbon dioxide as well.
Worldwide, plants are believed to respire 60 billion tons of CO2 each year. This is six times the quantities released by the combustion of oil, coal and gas to feed human economies. But how much does respiration increase with temperature?
The researchers measured plant response to temperature at 30-minute intervals at 231 different sites: from the Alaskan tundra to the boreal forests of Sweden and the temperate woodland of New York, the tropic regions of Peru, Costa Rica and French Guiana, and the savannahs of Texas and Australia.
They then modelled their results, to define a relationship. And they found that in the coldest regions, plants respired less than originally predicted.
“Some ecosystems are releasing a lot less CO2 than we previously thought,” says Kevin Griffin, professor of Earth and environmental sciences at Columbia University’s Lamont-Doherty Earth Observatory. “All this adds up to a significant amount of carbon, so we think it’s worth paying attention to,”
But high-latitude plants grow on soils that are home to billions of tonnes of organic carbon stored in the permafrost. As the world warms, plants are moving north and consuming more carbon from the atmosphere. But the same process is triggering microbial actions that could release once-frozen carbon from the Arctic tundra.
And a new study in Environmental Research Letters concludes that more carbon will be released by climate change than can be stored by trees and shrubs as they colonise more and more of the high latitudes.
A pooled estimate from 98 researchers concluded that if the world went on burning fossil fuels on a business-as-usual basis, then by 2100 five times more carbon would be released than new growth could store.
The carbon budget is not a new headache for climate science. Studies have tried to put a measure on the responses of the tropical forests and the permafrost. And while some teams have anxiously totted up the quantities of carbon dioxidereleased as greenhouse gases, others have tried to monitor the overall response of the living world to the extra fertilisation from additional CO2.
So the latest studies are more of the same: fresh approaches to aspects of one over-arching challenge.
The stakes are high. Disturbance to the permafrost could have catastrophic consequences, and much depends on life’s fundamental units − the soil microbes that break down organic materials, and release organic carbon from the permafrost, or the forest floor.
How resilient is the microbial world to climate change? To find out, researchers launched an experiment that involved digging some soil from a mountainside in Washington State.
They moved one sample 500 metres up hill, and another 500 metres downhill, and matched them against those native to the different altitudes. Now, 17 years later, they report in the Public Library of Science journal PLOS One that they measured the changes in enzyme activity and rates of respiration at their test sites.
Those microbes that had been transplanted hardly changed their ways, including their original rates of respiration. So microbial communities might not respond quickly to new conditions.
“With our changing climate, all microbes will be experiencing new conditions and more extremes,” says Vanessa Bailey, a biologist at Pacific Northwest National Laboratory.
“Climate change won’t translate simply to steady warming everywhere. There will be storm surges, longer droughts, but some places may end up experiencing more mild climates.
“This study gives us a glimpse of how microbes could weather such changes under one set of conditions. They may be constrained in surprising ways.”