Since carbon dioxide is an important greenhouse gas, one strategy that can partially combat global warming and climate change is to increase the amount of carbon stored in plants.  By increasing the amount of plant life on earth, or altering it to plant types that store the most carbon, more carbon dioxide may be pulled out of the air and stored for a period of time. 

Scientists call anything that removes carbon from the atmosphere a ’sink’.  In order to be effective in combating climate change, the sink must be large and the carbon must stay in the sink.  So what is important for climate change is not the amount of carbon exchanged between the atmosphere and plants, but how much carbon stays in the total forest and total grassland ’sinks’. 

Australia has 149 million hectares of forest.  Of this, 147 million hectares is native forest, dominated by eucalypt (79%) and acacia (7%), and 1.82 million hectares is in plantations[i]. Grassland covers around 440 million hectares of land in Australia[ii]. 

The size of the difference in the total carbon storage between grasslands and woodlands depends not just on the amount of land covered by the plants, but on the capacity of the individual ecosystems to store carbon, and the depth to which the carbon sink is tested.   The sinks can be the plant material above ground, below ground (roots), and soil that is enriched in carbon by dead plant material.

Based on data from typical perennial grasslands and mature forests in Australia, forests are typically more than 10 times as effective as grasslands at storing carbon on a hectare per hectare basis.

[i] Bureau of Rural Science, (2008) http://adl.brs.gov.au/forestsaustralia/facts/type.html

[ii] Australian Government, (2007), National Inventory Report Vol 2 Part g,  Department of Climate Changehttp://www.climatechange.gov.au/publications/greenhouse-acctg/~/media/publications/greenhouse-acctg/national-inventory-report-vol-2-part-g.ashx

Carbon in plants

Carbon is continuously exchanged between various elements of the earth: atmosphere, soil, ocean and life, which is predominately plant material.  The length of time it takes for the carbon to be exchanged depends on the process involved.  In the process known as photosynthesis, plants generate their own ‘food’ by absorbing carbon dioxide (CO2), water (H2O) and sunlight to create sugars.  Excess oxygen is released, and carbon is stored in the sugars and starches (particular combinations of carbon (C), hydrogen (H) and oxygen (O) in the plant material.

Forests

The amount of carbon taken up every year by dry forests in Australia depends on the weather conditions and age of the trees.  Science tells us that the range for forests with continuous canopies is about 0.5-2 tonnes of carbon per year for each hectare.  Grasslands may have a similar annual rate of net carbon uptake[i], but the long-term storage of carbon per hectare of grasslands is less than that over an average hectare in woody trees. 

In other words, over the long haul, more carbon stays in the tree sink than in the grass sink.  Some Australian native eucalyptus forests store up to ten times more carbon per hectare than Australian native and introduced grasslands – both above and below ground[ii]. 

The Co-operative Research Centre for Greenhouse Accounting has estimated that Australian forests store about 10.5 billion tonnes of carbon (excluding soil carbon)[iii].  This store of solid carbon has accumulated over an assumed life of 100 years for native eucalypt regrowth.  That translates to our forests storing an amount of carbon equivalent to almost 38.5 billion tonnes of gaseous carbon dioxide from the atmosphere, about 70 times Australia’s annual net greenhouse gas emission. 

Grasses

Using data from a study of semi-arid Australian grasslands by the Queensland Department of Primary Industry[iv] that accounted for the amount of live grass above ground found that about 5 tonnes of carbon could be stored per hectare of perennial grass year, assuming little grazing.  This compares to carbon stocks of mature dry sclerophyll forest that contain about 100 tonnes of carbon per hectare (with wide variability).  A recent ANU study assembling data from Australia’s unlogged, natural eucalypt forests concluded that kind of ecosystem may even hold an average of 640 tonnes of carbon per hectare[v].

So, in order for grasslands to have a greater carbon stock than an equivalent acreage of Australian forest, the roots of a summer pasture grass such as kangaroo grass, panic or weeping grass, would have to contain more than 10 times the mass of the grass that you can see above the ground[vi], which is not the case.

Soil carbon

Carbon can also be stored in the soil itself in the form of old organic matter.  Depending on the depth of soil investigated, the nutrient level of the soil and the availability of water, grassland soil can have either a similar or much lower amount of carbon than does the soil beneath forests.

As an example, studies done in 1999[vii] and again in 2005 show that reducing the amount of tree cover tends to decrease the amount of organic carbon in deep soil sinks[viii].  The 2005 study showed that about 1 metre underground, grassland sites contained only 25 tonnes of carbon in the soil per hectare compared with the soil in treed savannah sites, which stored 30 to 70 tonnes per hectare. 

The NSW Department of Primary Industry has compared soil organic carbon under perennial pasture in high rainfall areas in the mid-north coast of NSW to native hardwood forests within a 100km radius.  They found that for the high-rainfall areas studied, there was no significant difference between soil organic carbon in the pastures and native forests at 20 centimetres depth, with an average storage of 72.9 tonnes per hectare in the pasture versus 76.5 tonnes per hectare in the native forest sites[ix].

[i] Potter KN, Potter SR, Atwood JD and Williams JR, (2004) Comparing Simulated and Measured Soil Organic Carbon Content of Clay Soils for Time Periods Up to 60 Years, Environmental Management Vol. 33, Supplement 1, pp. S457–S461,  http://www.springerlink.com/content/8u6h76lr73p8eh6c/ 

Potter, K. N.; Torbert, H. A.; Johnson, H. B.; Tischler, C. R. (1999), Carbon Storage After Long-Term Grass Establishment on Degraded Soils, Soil Science: October 1999 – Volume 164 – Issue 10 – pp 718-725 http://journals.lww.com/soilsci/Abstract/1999/10000/Carbon_Storage_After_Long_Term_Grass_Establishment.2.aspx

Scurlock, J.M.O.; Johnson, K. and Olson, R.J. (2002). “Estimating net primary productivity from grassland biomass dynamics measurements”. Global Change Biology 8: 736. doi:10.1046/j.1365-2486.2002.00512.x, http://www3.interscience.wiley.com/journal/118961406/abstract?CRETRY=1&SRETRY=0 

[ii] Mackey BG, Keith H, Berry SL and Lindenmayer DB, (2008) Green Carbon – The role of natural forests in carbon storage, A green carbon account of Australia’s south-eastern Eucalypt forest, and policy implications, ANU E Press, http://epress.anu.edu.au/green_carbon/pdf/whole_book.pdf 

Keith H, Mackey BG and Lindenmayer DB, (2009), Re-evaluation of forest biomass carbon stocks and lessons from the world’s most carbon-dense forests, PNAS Early Edition,  http://www.pnas.org/content/early/2009/06/24/0901970106.full.pdf

[iii] Ximenes F, Robinson M, and Wright B, (2007) Forests, Wood and Australia’s carbon balance, Australian Government Forest and Wood Products Research and Development Corporation and Cooperative Research Centre for Greenhouse Accounting , http://www.plantations2020.com.au/assets/acrobat/Forests,Wood&CarbonBalance.pdf

[iv] Christie EK, (1981), Biomass and nutrient dynamics in a c4. semi-arid Australian grassland community,  Journal of Applied Ecology (1981), 18, 907-918, http://www.jstor.org/pss/2402381

[v] Mackey BG, Keith H, Berry SL and Lindenmayer DB, (2008) Green Carbon – The role of natural forests in carbon storage, A green carbon account of Australia’s south-eastern Eucalypt forest, and policy implications, ANU E Press, http://epress.anu.edu.au/green_carbon/pdf/whole_book.pdf 

[vi] CSIRO Sustainable Agriculture Flagship, (2009), An Analysis of Greenhouse Gas Mitigation and Carbon Sequestration Opportunities from Rural Land Use, edited by Sandra Eady, Mike Grundy, Michael Battaglia and Brian Keating, http://www.csiro.au/files/files/prdz.pdf

[vii] Boutton T W, Archer S R and Midwood A J 1999 Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical Savanna. Rapid Commun. Mass Spectrom. 13, 1263–1277

[viii] Chen X, Hutley LB and Eamus D, (2005), Soil organic carbon content at a range of north Australian tropical savannas with contrasting site histories, Plant and Soil, Volume 268, Number 1 / January, 2005, http://www.springerlink.com/content/p0123502p0515w05/ 

[ix] McCoy D, Ky C, (2009) Australian Society for Soil Science Inc, http://www.asssi.asn.au/downloads/soils2008/Tu42%20107-G-McCoy%20et%20al.pdf

The world is at a crossroads.

We must contain and then reduce our greenhouse gas emissions so that our farmers, graziers and fishermen have the best chance to feed the world, and our industries have the best opportunities for sustainable growth and new green markets.

So that we – along with the rest of Earth’s inhabitants – are best able to flourish in good health, and the world’s poorest have the best opportunity for hope.

The leading climate scientists from the world over warn that we have about five years to avoid the dangerous climate change that would be generated if average global temperatures increase by more than 2°C above pre-industrial levels.

Australia will be one of the most affected regions in the world if we exceed this ‘guardrail’ temperature.

For example, regional climate change projections indicate that we are likely to see an increase in the frequency and intensity of wildfires (predominately in south-eastern Australia), an increase in the severity of cyclones, decreased rainfall (except in the far north), increased incidence of drought, and an increase in extreme temperatures. 

To avoid hitting the guardrail, annual global emissions must reverse from increasing every year, as they do now, to decreasing every year.

The globe has warmed by nearly 0.8°C over pre-industrial levels. Global temperatures will increase by another 0.5°C as the Earth continues to react to the emissions that we have already emitted in the atmosphere, much of which lingers there for a century or more.

Taken together, this means that climate change corresponding to a 1.3°C temperature rise is now ‘locked in’. Our previous actions have already placed us more than half way to the 2°C guardrail, and yet rather than putting our foot on the brake, we have it on the accelerator.

The greenhouse effect

The sun continuously bathes the Earth with energy in the form of sunlight. Much of this energy is absorbed by the Earth, and then emitted as infrared radiation, or heat. Greenhouse gases prevent the Earth from discarding as much of this heat as it otherwise would back into space.

Without naturally occurring greenhouse gases, the Earth would be a much colder place, inhospitable to modern human existence. But by the same token, the additional greenhouse gases added to this store by humans is slowly increasing the average temperature of the Earth system.

Due to the quantity in which it is emitted by humans, its longevity in the atmosphere, and its effects in trapping heat, carbon dioxide is the most important of the greenhouse gases currently causing changes in the Earth’s climate.

While the growth of human carbon dioxide emissions slowed in 2008, a slight reprieve attributed to the global financial crisis, they are still tracking above the worst-case scenario considered by the Intergovernmental Panel on Climate Change (IPCC) in their 2007 report.

In fact, atmospheric levels of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are higher now than at any time since modern humans have evolved.

Too much energy

This growing store of greenhouse gases, is leading to extremes in our weather and changing the long-term climate. Summers are becoming hotter, and droughts are longer and drier. The oceans are becoming more acidic. Sea levels are rising as glaciers melt and the warmer water expands.

If we do not act now, the newest and best science indicates that the average global sea level in 2100 will be 75 to 190 centimetres above 1990 levels, and continue to rise thereafter.

In Australia, extreme fire danger days are already becoming more numerous in many parts of the country, and floods and cyclones more intense.

Research by the CSIRO indicates that the frequency of days with very high and extreme Forest Fire Danger Index ratings is likely to increase by 15 to 70 per cent by 2050 in southeast Australia.

With much of Earth’s biosphere already ‘feeling the heat’, the Great Barrier Reef ecosystem is in grave danger both due to increased water temperatures, and increased acidification as the ocean absorbs some of the additional carbon we have placed in the atmosphere.

Changes have been observed in the breeding and migratory patterns of birds, fish and animals; and plant species have spread into latitudes that were previously too cold for them.

Reaching a limit

Why is limiting the average global temperature rise to 2°C so important?

The primary answer is it will be very difficult to adapt to and thrive in temperatures any higher.

As a single example, an increase of surface wind speed of 5 metres per second, made possible with a 1°C rise in ocean temperature, would double the frequency of Category 5 tropical cyclones.

In 2006 Cyclone Larry, a marginal Category 5 cyclone, devastated approximately 12,500 square kilometres around the far north Queensland town of Innisfail and destroyed the region’s banana industry.

Exceeding the 2°C guardrail will also reduce Earth’s limited ability to counteract some of the effects of climate change. If the temperature rise is 2.5°C or more, land ecosystems may emit carbon rather than absorb it, contributing to rather than acting as a buffer against climate change.

Already, the fraction of anthropogenic carbon dioxide that is absorbed by the ocean ’sink’ (a form of ‘free’ climate change mitigation) has decreased in last 50 years, for reasons that scientists are still studying.

Time is short

And why must we act quickly?

Calculations catalogued by the 2007 IPCC report tell us that if global temperature rise is to be kept between 2.0 and 2.4°C, then the ‘CO2 equivalent’ concentration, which is used as a combined measure of all Kyoto greenhouse gases, must not be allowed to exceed the range between 445 and 490 parts per million (ppm).

Current CO2 equivalent emissions are 455 ppm and rising.

To meet the 2°C guardrail target, we must halt increases in global CO2 equivalent emissions by about 2015, and then decrease them dramatically and steadily thereafter. 

Around the world, individuals, communities and nations are implementing effective strategies to do their part to effect this change. Australians have a leading part to play in demonstrating how this can be done even in a society known for having the highest carbon emissions per capita. But we need more shoulders at the wheel, because time is short and the clock is ticking – loudly.

This article can be found on the ABC Science website.

On the eve of the Copenhagen, Professor Sackett says that two things are certain regardless of the outcome of the summit.

“First, the scientific truths that have set the world on this common journey are tolling more clearly than ever the need to take immediate action on climate change.  

“Second, an incredible amount of work will still remain to be done in the wake of Copenhagen, most of it outside the realm of politics.

“The clock is ticking loudly for the world.  If we wait until 2020 to turn the annual emissions curve over from increasing every year to decreasing, we will need to either clip global emissions by a hefty 9% per year, or prepare ourselves for a considerably warmer and more severe world,” Professor Sackett said.  .

The importance of research and scientific evidence to inform Government policy will permeate Professor Sackett’s address.

“Science is at the base of this issue, it is important to review what the latest science tells us about the extent and speed of climate change.

 “Already we have committed our future to one in which the global average temperature will be 1.3 degrees higher than in pre-industrial times; even if everyone on the face of the Earth stops emitting greenhouse gases tomorrow.

“Australia must develop individual and community-based pro-active, ‘bottom up’ practices that will enhance our national and global collective responsibility on climate change” Professor Sackett said.   

Speaking about the Chief Scientist, host of the event Michael Roux, Executive Chairman of the Australian Davos Connection (ADC) said, “Professor Penny Sackett s the leading expert in this country who can effectively bridge the gap between science and policy, translating our knowledge of the science into urgent policy imperatives.

“This is an opportunity to hear directly from Professor Sackett, during a critical time for the future of our environment, what the latest research is telling us about climate change and what we can do to reduce greenhouse gas emissions in Australia and overseas.

Click here to download media release

Media Contact: Rebecca Richter, Office of the Chief Scientist
Mobile: 0410 029 407

Moving the World -- Science and leadership before and after Copenhagen

Presentation Slides

Video Highlights:

In Copenhagen on March 10-12 2009, the International Alliance of Research Universities came together to discuss the latest international scientific consensus on climate change. The result was this report featuring six key messages and conclusions which detail how we must continue to address the increasing challenges posed by climate change into 2010 and beyond.

Climate Change: Global Risks, Challenges and Decisions

For further information, please visit: www.climatecongress.ku.dk

The data shows that more and larger fires can be predicted if we cannot change the trajectories of global warming. The Chief Scientist will explore the ways in which science can help us predict the frequency of bushfire weather in the future, as well as avoid or adapt to more frequent and more intense fires in the future.

While bushfires are part of Australia’s natural environment, we can help damaged ecosystems so they adapt more quickly after fires by enhancing their resilience through ecological engineering.

Science can also help with human recovery – not only helping rebuild infrastructure and redesigning suburbs so that homes and other buildings are less at risk from bushfires, but also with the recovery of people after a fire. Both the physical and emotional scars left by bushfires are potent and debilitating. It is hoped that science can assist many on their long and difficult recovery from trauma.

The full speech can be viewed or listened to below:

Our future climate – living with fires now and into the future

“Engaging with international counterparts on topical science issues is essential in order for us to find global solutions to global problems such as climate change and emerging health issues,” Professor Sackett said.

While in the United States, Professor Sackett met with key officials including:

• Dr Harold Varmus, co-chair of the President’s Council of Advisors on Science and Technology (PCAST);
• Dr John Holdren, Director, Office of Science and Technology Policy, Executive Office of the President; and co-chair of PCAST;
• Dr Nina Federoff, Special Advisor (Science and Technology), US Department of State;
• Dr Arden Bement, Director, National Science Foundation; and
• Dr Jane Lubchenco, Under Secretary of Commerce for Oceans and Atmosphere; and Administrator for National Oceans and Atmospheric Administration (NOAA).

“We discussed issues common to our two countries, and the rest of the global community, including climate change, clean energy research and best practice approaches for providing expert advice to Government.

“It is only through engagement across geographical and societal boundaries and across scientific disciplines that we will be able to find solutions to these issues and implement them,” Professor Sackett said.

Professor Sackett will be talking further about the importance of collaboration to find global solutions to global problems at the Cooperative Research Centre (CRC) Pathfinders Conference on Wednesday 27 May at the Canberra Convention Centre.

For more information on Professor Penny Sackett’s speaking engagements refer to www.chiefscientist.gov.au.

Click here to download media release

Media Contact: Rebecca Richter, Office of the Chief Scientist
Mobile: 0410 029 407

Engaging in a changing climate