Second in a series
The IPCC's Special Report on Climate Change and Land, released this month, promotes sustainable land management practices as the most important way to maintain the health of the land - but time might be running out.
The United Nations Intergovernmental Panel on Climate Change warned last year that unless we limit warming to 1.5 degrees, the only ways of stabilising the climate will involve large amounts of land use change and efforts to withdraw carbon dioxide from the atmosphere, UNE scientist Annette Cowie, one of the report's co-authors, said.
"The main ways that we can see for [withdrawing CO2 from the atmosphere] are things like planting trees and building soil organic matter, which are very beneficial - but they can only do a small amount of the job," Professor Cowie said.
Reforesting nearly 1 billion hectares of unused land worldwide could pause global warming by 20 years, trapping two-thirds of the amount of carbon released since the Industrial Revolution, a study in Science magazine (July) claimed.
Trees can also restore dry land - a valuable technique in a country like Australia that suffers from desertification, as farmers in Western Australia facing dryland salinity have discovered.
The farmers had overcleared their land, and the saline water table had diminished the growth of their wheat, Professor Cowie explained. Planting mallee eucalypts in strips across the landscape can draw down the water table, increasing wheat productivity.
Trees can also be used as shelterbelts to enhance lamb survival or control wind erosion.
"We certainly need them in the New England region," Professor Cowie said.
Building organic matter takes carbon dioxide out of the atmosphere, and stores it in the land, she explained. Biochar - charcoal made from different types of biomass - can reduce soil emissions of methane and nitrous oxide, more powerful greenhouse gases than carbon dioxide.
Farmers can also rotate crops, and keep stubble on site, rather than burning it, Professor Cowie advised. They should also include pasture in the crop rotation, as mixed farming systems with livestock and cropping can be more sustainable.
These sustainable land management practices can avoid, or even reverse and reduce degradation. Not only they return land to productivity, and provide ecosystem services, Professor Cowie said, but they build organic matter again, taking more carbon dioxide out of the atmosphere.
But Professor Cowie doubts they will be enough.
"If we continue to release greenhouse gases from fossil fuels, we're going to need more drastic measures," she said.
Such as biofuels - renewable power sources that can be burnt to produce heat and power, with carbon capture and storage.
The future might see us growing biomass (energy crops, such as canes) over large areas of the landscape, burning it in power stations, collecting the carbon dioxide, and putting it underground.
"It's one of the main ways of sequestering carbon that scientists suggest will be required in large amounts if we don't address climate change very soon," Professor Cowie said.
The drawback is that it will need a lot of land - and good land governance.
"We need to make sure that it's done well; we need to start planning for it now," Professor Cowie said.
"In order to tackle the climate change issue, and to meet the target of constraining warming to less than two degrees, we need to balance emissions by removals - that is, sequestration - by the middle of the century.
"So we need to aim for net zero across the globe by the middle of the century. We're going to need to use a lot of land for this purpose.
"So we're going to need to develop ways to fix carbon in the landscape; take carbon out of the air; and put it into our land in the form of vegetation and soil organic matter.
"And we're going to need policies that encourage that action - and the sooner the better."
Professor Cowie is adjunct professor at UNE's School of Environmental and Rural Science, and principal climate research scientist at the NSW Department of Primary Industries. She is task leader of an International Energy Agency Bioenergy research network; land degradation advisor on the Scientific and Technical Advisory Panel of the Global Environment Facility; and a member of the Science Policy Interface of the UN Convention to Combat Desertification.