Thursday, July 4, 2013

The foliage on native plants in Australia's arid zones is boosted by CO2

Increased levels of carbon dioxide (CO2) have helped boost green foliage across the world’s arid regions over the past 30 years through a process called CO2 fertilisation, according to CSIRO research.

In findings based on satellite observations, CSIRO, in collaboration with the Australian National University (ANU), found that this CO2 fertilisation correlated with an 11 per cent increase in foliage cover from 1982-2010 across parts of the arid areas studied in Australia, North America, the Middle East and Africa, according to CSIRO research scientist, Dr Randall Donohue.

"In Australia, our native vegetation is superbly adapted to surviving in arid environments and it consequently uses water very efficiently," Dr Donohue said. "Australian vegetation seems quite sensitive to CO2 fertilisation.

The fertilisation effect occurs where elevated CO2 enables a leaf during photosynthesis, the process by which green plants convert sunlight into sugar, to extract more carbon from the air or lose less water to the air, or both.
This, along with the vast extents of arid landscapes, means Australia featured prominently in our results."

"While a CO2 effect on foliage response has long been speculated, until now it has been difficult to demonstrate," according to Dr Donohue.

"Our work was able to tease-out the CO2 fertilisation effect by using mathematical modelling together with satellite data adjusted to take out the observed effects of other influences such as precipitation, air temperature, the amount of light, and land-use changes."

The fertilisation effect occurs where elevated CO2 enables a leaf during photosynthesis, the process by which green plants convert sunlight into sugar, to extract more carbon from the air or lose less water to the air, or both.

If elevated CO2 causes the water use of individual leaves to drop, plants in arid environments will respond by increasing their total numbers of leaves. These changes in leaf cover can be detected by satellite, particularly in deserts and savannas where the cover is less complete than in wet locations, according to Dr Donohue.

"On the face of it, elevated CO2 boosting the foliage in dry country is good news and could assist forestry and agriculture in such areas; however there will be secondary effects that are likely to influence water availability, the carbon cycle, fire regimes and biodiversity, for example," Dr Donohue said.

"Ongoing research is required if we are to fully comprehend the potential extent and severity of such secondary effects."

This study was published in the US Geophysical Research Letters journal and was funded by CSIRO's Sustainable Agriculture Flagship, Water for a Healthy Country Flagship, the Australian Research Council and Land & Water Australia.

Reprinted from CSIRO

Donohue, R. J., M. L. Roderick, T. R. McVicar, G. D. Farquhar. 2013 "Impact of CO2 fertilization on maximum foliage cover across the globe's warm, arid environments. Geophys. Res. Lett. 40, doi:10.1002/grl.50563

Non-deciduous perennials are responding better than deciduous, annual and ephemeral plants

Here is the abstract from a previous paper by Dr Donohue (my paras):

Using Advanced Very High Resolution Radiometer data spanning 1981–2006 and calibrated for long-term analyses of vegetation dynamics, we examine whether vegetation cover has increased across Australia and whether there has been a differential response of vegetation functional types in response to changes in climatic growing conditions. Trends in vegetation cover are interpreted within Budyko's energy – water limitation framework.

Results from an Australia-wide analysis indicate that vegetation cover (as described by the fraction of Photosynthetically Active Radiation absorbed by vegetation; fPAR) has increased, on average, by 0.0007 per year – an increase of ∼8% over the 26 years. The majority of this change is due to a 0.0010 per year increase in persistent fPAR (representing nondeciduous perennial vegetation types; up 21%).

In contrast, recurrent fPAR (representing deciduous, annual and ephemeral vegetation types) decreased, on average, by 0.0003 per year (down 7%), the trends of which are highly seasonal.

Over the same period, Australian average annual precipitation increased by 1.3 mm yr−2 (up 7%).

A site-based analysis using 90 long-term meteorological stations with minimal localized land-cover changes showed that energy-limited sites where total fPAR increased generally experienced decreases in precipitation, and water-limited sites that experienced decreases in cover were almost always associated with decreases in precipitation.

Interestingly, where vegetation cover increased at water-limited sites, precipitation trends were variable indicating that this is not the only factor driving vegetation response. As Australia is a generally highly water-limited environment, these findings indicate that the effective availability of water to plants has increased on average over the study period. Results also show that persistent vegetation types have benefited more than recurrent types from recent changes in growing conditions.

Regardless of what has been driving these changes, the overall response of vegetation over the past 2–3 decades has resulted in an observable greening of the driest inhabited continent on Earth.

Wednesday, May 29, 2013

The Heat is On....Stop Procrastinating, People

Don't take comfort from the Bayesians or other low estimates of climate sensitivity - this study says it's going to get bad, and worse if we don't act now...

Uncertainty no excuse for procrastinating on climate change

By Roger Bodman, Victoria University and David Karoly, University of Melbourne

Today we released research which reduces the range of uncertainty in future global warming. It does not alter the fact we will never be certain about how, exactly, the climate will change.

We always have to make decisions when there are uncertainties about the future: whether to take an umbrella when we go outside, how much to spend on insurance. International action on climate change is just one more decision that has to be made in an environment of uncertainty.

The most recent assessment of climate change made by the Intergovernmental Panel on Climate Change in 2007 looked at what is known with high confidence about climate change, as well as uncertainties. It included projections of future global warming to the end of this century based on simulations from a group of complex climate models.

These models included a range of uncertainties, coming from natural variability of the climate and the representation of important processes in the models. But the models did not consider uncertainty from interactions with the carbon cycle – the way carbon is absorbed and released by oceans, plant life and soil. In order to allow for these uncertainties, the likely range of temperature change was expanded.
Our recent study has re-visited these results and tested an approach to reduce the range of uncertainty for future global warming. We wanted to calibrate the key climate and carbon cycle parameters in a simple climate model using historical data as a basis for future projections. We used observations of atmospheric carbon dioxide concentrations for the last 50 years to constrain the representation of the carbon cycle in the model. We also took the more common approach of using global atmospheric and ocean temperature variations to constrain the response of the climate system.

This led to a narrower range of projected temperature changes for a given set of greenhouse gas emissions. As a consequence, we have higher confidence in the projections. In other words, using both climate and carbon dioxide observations reduces the uncertainties in projections of global warming. (Click the chart to enlarge it.)

Figure 1. Global-mean temperature change for a business-as-usual emission scenario, relative to pre-industrial. Black line: median, shaded regions 67% (dark), 90% (medium) and 95% (light) confidence intervals. The sidebars are uncertainty ranges based on the IPCC likely range and best estimate (grey column) for 2090-2099 and our corresponding results (purple column) from the simple climate model (MAGICC); the black bars are the respective best estimates (modified from Nature Climate Change paper). Bodman & Karoly

We found that uncertainties in the carbon cycle are the second-largest contributor to the overall range of uncertainty in future global warming. The main contributor is climate sensitivity, a measure of how the climate responds to increases in greenhouse-gas concentrations.

Climate sensitivity has been discussed recently on The Conversation. A recent study by Alexander Otto of Oxford University and colleagues, published in the journal Nature Geoscience, also considered future global warming in the context of observations of global mean temperature change over the last decade.
Unlike that study, our results do not show lower climate sensitivity or lower mean projected global warming. Our study uses the same observed global atmospheric and ocean temperature data. But we also used observed carbon dioxide data and represented important additional processes in our simplified climate model, particularly the carbon cycle on the land and in the ocean and uncertainties in the climate forcing due to aerosols.

In our study, the reductions in uncertainty came from using the observations, the relationships between them and how these affect the parameters in the simple climate model. We found 63% of the uncertainty in projected warming was due to single sources, such as climate sensitivity, the carbon cycle components and the cooling effect of aerosols, while 37% of uncertainty came from the combination of these sources.
Once we reduced the uncertainty we found there is an increased risk of exceeding a lower temperature change threshold, but a reduced chance of exceeding a high threshold. That is, for business-as-usual emissions of greenhouse gases, exceeding 6°C global warming by 2100 is now unlikely, while exceeding 2°C is virtually certain.

These results reconfirm the need for urgent and substantial reductions in greenhouse gas emissions if the world is to avoid exceeding the global warming target of 2°C. Keeping warming below 2°C is necessary to minimise dangerous climate change.

It is unlikely that uncertainties in projected warming will be reduced substantially. Indeed, if you allow for population growth, levels of economic activity, growth in demand for energy and the means of producing that energy, overall uncertainty increases. We just have to accept that we will have to manage the risks of global warming with the knowledge we have. We may not know exactly how much and by when average temperatures change, but we know they will. This is an experiment we probably don’t want to make with the only planet we have to live on.

Roger Bodman received funding from the Australian Research Council while completing his PhD.
David Karoly receives funding from the Australian Research Council and the Australian Antarctic Division. He is a Chief Investigator in the ARC Centre of Excellence for Climate System Science, a member of the Climate Change Authority and a member of the Science Advisory Panel to the Climate Commission.

The Conversation
This article was originally published at The Conversation. Read the original article.