Earth greening despite deforestation

05 Apr, 2015 01:00 AM
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Observations from space have shown the world overall is getting greener despite deforestation and drought. Photo: Carl Davies/CSIRO
Australia is 'greener' today than it was two decades ago. This is despite ongoing land clearing
Observations from space have shown the world overall is getting greener despite deforestation and drought. Photo: Carl Davies/CSIRO

WHILE the news coming out of forests is often dominated by deforestation and habitat loss, research published in Nature Climate Change shows that the world has actually got greener over the past decade.

Despite ongoing deforestation in South America and South East Asia, we found that the decline in these regions has been offset by recovering forests outside the tropics, and new growth in the drier savannas and shrublands of Africa and Australia.

Plants absorb around a quarter of the carbon dioxide that people release into the atmosphere by burning fossil fuels. With a greening globe, more plants may mean more absorption of carbon dioxide. If so, this will slow but not stop climate change.

However, questions remain over how long plants can keep pace with our increasing emissions in a warmer climate.

Measuring carbon in plants

We studied how plants and vegetation are faring by determining the amount of carbon stored in living plant mass (or 'biomass') above the ground.

We developed a new technique to map changes in vegetation biomass using satellite measurements of changes in the radio-frequency radiation emitted from the Earth’s surface, a technique called passive microwave remote sensing. The radiation varies with temperature, soil moisture and the shielding of water in vegetation biomass above the ground.

We extracted this vegetation information from several satellites and merged them into one time series covering the past two decades. This allowed us to track global changes in biomass from month to month, something that was not possible before.

For the period 2003-12, we found that the total amount of vegetation above the ground has increased by about four billion tonnes of carbon.

Still losing rainforests, but gaining forests elsewhere

Our global analysis shows losses of vegetation in many regions, particularly at the frontiers of deforestation in the tropics of South America and South East Asia.

As expected, the greatest declines have been in the so-called 'Arc of Deforestation' on the southeastern edge of the vast Amazon forests. In South East Asia we found the most widespread declines in the Indonesian provinces of Sumatra and Kalimantan - the Indonesian part of Borneo.

However, we found that these rainforest losses have been offset by increases in biomass in other parts of the world.

For example, forests have spontaneously regrown on farmland abandoned after the fall of communism in Russia and neighbouring countries, while large-scale tree planting projects in China have measurably added to the global biomass. This roughly offset half of the carbon loss by tropical deforestation.

We also found unexpectedly large vegetation increases in savannas and shrublands of Australia, Africa, and South America. Previous analyses have focused on closed forests and did not measure this increase.

Is Australia getting greener?

On average, Australia is 'greener' today than it was two decades ago. This is despite ongoing land clearing, urbanisation and the recent droughts in some parts of the country.

However, the increase in vegetation has not been uniform. The largest increases are in northern Australia, with lesser increases in southern Australia and a small decrease in southeastern Australia.

Mean annual change in vegetation biomass between 1993 and 2012. Blue represents an increase; red a decrease. (Image modified from Liu et al., 2015)

These vegetation trends seem to be mainly explained by rainfall patterns: northern Australia has been getting wetter and southeast Australia dryer. This pattern is predicted to continue according to the most recent climate change projections from the CSIRO and the Bureau of Meteorology.

Australian vegetation growth generally responds strongly to rainfall variations. More variability and an apparently increasing frequency of extreme El Nino and La Nina events due to climate change would create stronger boom-bust cycles in Australia’s vegetation.

Apart from the effect of rainfall patterns, our study also agreed with other studies observing a gradual greening trend for the past two decades, even where there was no change or even a small decrease in rainfall.

This has been ascribed mainly to the increasing number of trees and shrubs growing on semi-arid grasslands. These plants are more efficient water users than other plants such as grasses. With the increased atmospheric concentration of carbon dioxide from fossil fuel emissions, they are able to absorb more carbon from the atmosphere without using more water.

More vegetation will slow but not prevent climate change

The world’s vegetation plays an important role in slowing down climate change. About a quarter of all carbon emissions from human activities are removed by terrestrial vegetation, with the size of the carbon land sink increasing over time.

However, it remains to be seen how the increased climate variability that accompanies climate change will affect this terrestrial 'carbon sink' in future. This is particularly true for seasonally dry ecosystems that experience fires, such as Australia’s savannas, where a single fire event can easily remove the carbon stored in plant biomass over many previous years. The future interaction between climate variability, vegetation and fire is difficult to predict and remains the focus of intense research.

Overall, our study provides more direct evidence of the global increase of vegetation growth and the terrestrial carbon sink than previous studies, with unprecedented geographical attribution and year-to-year changes.

With terrestrial vegetation removing about a quarter of the carbon emissions from human activities and the global oceans removing another quarter, this means that half of our CO2 emissions remains in the atmosphere. Therefore, stabilising concentration of CO2 in the atmosphere and the consequent impact on the climate system will still require large reductions of global fossil fuel emissions.


The Conversation

This article was originally published on The Conversation.

Read the original article.

Yi Liu and Albert Van Dijk are from the Australian National University, and Pep Canadell is from the CSIRO

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READER COMMENTS

m
5/04/2015 5:44:45 PM

im curious, why cant science come up with a genetically engineered tree that absorbs vast amounts of carbon- so a very fast growing tree that can absorb vast amounts of carbon and then we can cut the tree down and use the timber and then replant to start the cycle again?!?!
iggi
5/04/2015 6:17:35 PM

Who actually says that ElNino and LaNina events - humongous cycles in movement of the oceans - are intensified by climate change? Conversely, the strong predominance of ElNinos, including the whopper of 1978/9 look more likely to have upped Earth's temperature a notch.
Barcoo
6/04/2015 1:08:18 AM

An interesting story. Much of the red area seems to be in NSW. The suggestion is made that this is due to ongoing land clearing. Who the hell gets a permit to clear land in NSW? We are told that sustainability is the goal we are to aim for. There is absolutely nothing sustainable in the present model of unlimited consumption of fossil fuels and the closing down of agriculture as a way of mitigating the effects of unlimited consumption.
Old Crow
6/04/2015 10:38:24 AM

And whats wrong with having an atmospheric carbon dioxide rate of 500 , 600 , 700 or 800 ppm ? Absolutly nothing . You would not even realise the difference except at 800ppm your average veggi patch would be growing about 50% better. All plants would be greener and bigger.
Craniologist
6/04/2015 7:11:27 PM

Wonderful assumption,s Old Crow. Pity you don't understand the limitations of plant growth to increased heat and lack of necessary increased water availability. Basic plant physiology would give you a better understanding. Also, with the increased heat comes the extra variability of the climate. Never mind, one day it might dawn on you, you are so far behind the eight ball when it comes to being able to see the big picture, it will be a mammoth task for you to catch up. But really, it is doubtful if you ever will.
Old Crow
7/04/2015 6:52:23 AM

Wonderful assumptions, Craniologist. Pity you don't understand the limitations of CO2's heating effect to the atmosphere. Pity you also don't understand that plants have an improved water use efficiency when they are growing in higher CO2. Basic plant physiology does not seemed to have helped you. Pity you don't understand that increased amounts of atmospheric CO2 have a minuscule effect on the temperature as shown now over the last 20 years with zero increase in warming but rising CO2 rates. Pity you don't understand that warm is good and cold is bad. Never mind, one day it might dawn on you.
Gumtree
7/04/2015 7:05:08 AM

So the science and this article is wrong is it, Craniologist? There has been no greening of earth from increasing atmospheric carbon dioxide? Somehow I don't think much has dawned on you.
Old Crow
7/04/2015 8:33:20 AM

A little reading and refresher course for those with their head encased in concrete. http://www.climatedepot.com/2015/ 04/06/global-warming-pause-contin ues-temperature-standstill-length ens-to-18-years-4-months/
E. J.
7/04/2015 10:05:09 AM

There still seem to be some who believe IPCC propaganda. The IPCC is a body of 2500 Government (political) apointees. Whereas to date over 31,000 scientists, over 9000 with PhDs, have signed the Global Warming Petition Project debunking the theory of man-made global warming. Satelite data shows there has been no warming for 18 years, nor have sea levels risen in that time. In spite of propaganda we had a cool summer. Just ask the rice growers. They were concerned about the cold reducing their crop. Yes it was hot at Tibooburra and Marble Bar but whats new about that?
nico
7/04/2015 2:18:20 PM

EJ, where do you get what you present as "facts"? The Petition which you cite was debunked as a fraud a decade ago (especially as it was accompanied by a fraudulent letter, purporting to come from the US Academy). Satellite data does NOT show that there has been no warming. Sea levels have continued to rise. Get your facts from the science, EJ, not from denialist blogs, then we can have a rational discussion. See: http://www.cmar.csiro.au/sealevel /
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