Climate Change Expert Supports Agriculture’s Role in Reducing CO2
Agricultural practices should play an important part in climate change strategies, said Dr. James Hansen, director of NASA’s Goddard Institute for Space Studies. The physicist and climatologist known for predicting global warming in 1988 delivered the keynote address at the 2008 Kansas Wind & Renewable Energy Conference in Topeka.
Hansen said that time is growing short to keep climate change from reaching a dangerous tipping point, beyond which climate change will continue to occur even without any additional increases in greenhouse gas (GHG) levels. There can be no doubt that the main driving factor in climate change is the increase in GHGs from human activities, he stressed.
The primary GHGs include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Of all the GHG emissions, CO2 is the single largest climate “forcing.” A forcing is a change in the planet’s energy balance, which tends to alter global temperature. It is critical to control CO2 emissions soon, before it’s too late, he said.
Carbon dioxide has already increased from a preindustrial level of 280 parts per million (ppm), to 383 ppm in 2007, and it is now increasing by about 2 ppm per year. The dangerous level of CO2, at which we will set in motion unstoppable changes, is at most 450 ppm, Hansen said. The goal must be far lower than that, he added. In fact, the goal should be less than the current level.
“We must adopt policies that take the planet’s atmosphere back to a CO2 level of 350 ppm or less. The acceptable level of atmospheric CO2 will depend upon how well we do in reducing other greenhouse gases,” he said.
Why does the CO2 level need to be lower than it is today? Humanity and natural ecosystems adapted to the climate and the sea level that has existed for the past 12,000 years during the Holocene period, Hansen explained. This climate developed under atmospheric CO2 levels of about 280 ppm. Civilization’s infrastructure was built under this general climate structure, and depends on the stable sea level that has existed during this period.
Global temperatures are currently on the verge of extending beyond the bounds of anything seen so far during this period, he said. Global temperature is increasing by about 0.2°C per decade, with fluctuations from year to year, he noted. With rapid warming of 0.6°C in the past 30 years, global temperature is at its warmest level in the Holocene. “The ‘safe’ global temperature level is, at most, about 1°C greater than the year 2000 global temperature,” he said.
Sea level is now increasing at a rate of about 3 cm per decade or about one-third of a meter per century. This rate of sea level rise is about twice as large as the rate in the twentieth century. The main concern about sea level, however, is the likelihood that continued global warming could lead to ice sheet disintegration and much greater sea level increase. The prior interglacial period was warmer than the current one by at most 1°C on global average, yet sea level was as much as 4-6 meters higher. The last time that global surface temperature was as much as 2°C warmer than now was in the Pliocene, 3-5 million years ago, when sea level was about 25 meters higher. If all fossil fuels were burned, more than doubling the amount of CO2 in the air, the eventual global warming would be expected to exceed 3°C, possibly leading to an ice-free planet, as in the early Cenozoic, with sea level about 75 meters higher.
Figure 1. Temperature fluctuations over the past 400,000 years. The term “kyr BP” stands for “thousands of years before present,” so that -400 = 400,000 years ago.
Source: Jim Hansen, “Global Warming 20 Years Later: Tipping Points Near.” See: http://www.columbia.edu/~jeh1/
An examination of climate data beginning in 1850, from the Fourth Assessment Report of the U.N. Intergovernmental Panel on Climate Change, reveals that global average surface temperatures and sea levels are increasing, while Northern Hemisphere snow cover is decreasing.
Source: Fourth Assessment Report, U.N. Intergovernmental Panel on Climate Change
How can the goal of 350 ppm CO2 be reached? It will take a combination of actions, Hansen said, including help from agriculture and forestry.
“If CO2 emissions from coal were phased out over the period 2010-2030, and if use of unconventional fossil fuels (tar shale, tar sands) remained negligible, atmospheric CO2 would peak at 400-425 parts per million (ppm). In that case improved forestry and agricultural practices, especially reforestation, could get atmospheric CO2 back beneath 350 ppm within a century or less. During the overshoot phase we might hope that ocean and ice sheet inertia may keep climate impacts tolerable, avoiding the most disastrous effects. However, if coal use continues or expands, CO2 will be headed to the 500-600 ppm range, or even higher if unconventional fossil fuels such as tar shale are developed,” Hansen said. That is dangerous territory.
Hansen offers the following four-point strategy to avoid dangerous climate change.
1. Coal and unconventional fossil fuels must be curtailed and used only with capture and sequestration of the carbon dioxide underground. Existing coal-fired power plants should be phased out over the next few decades.
2. Carbon price and efficiency standards must be implemented. Recognizing the unusual energy concentration and mobility of fossil fuels — with which little else can currently compete — the practical way to transition to a post-petroleum era is to impose a moderate but continually rising carbon price. The price can be via a tax on fossil fuels, a ration-and-trade system that limits impacts on people least able to afford an energy tax, or a combination of methods. This will make fossil fuels pay for environmental damage while stretching remaining oil and gas to accommodate sustainable economic growth.
3. Steps must be taken now to draw down atmospheric CO2. Farming and forestry practices that enhance carbon retention in the soil and biosphere must be supported. Biofuel power plants with carbon sequestration can draw down atmospheric carbon dioxide, putting anthropogenic carbon dioxide back underground. Carbon dioxide can be sequestered beneath ocean sediments and in other safe geologic sites. Reforestation of degraded land and improved agricultural practices that retain soil carbon could draw down atmospheric CO2 by as much as 50 ppm. Additional significant CO2 reduction could be achieved by using carbon-negative biofuels to replace liquid fossil fuels and phasing out emissions from natural gas-fired power plants, according to the authors. A combination of these approaches could bring CO2 back to 350 ppm well before the end of the century.
4. We must take steps to reduce other, non-CO2 forcings, especially black soot, methane, and ground-level ozone via stricter regulations.
The next President must make a national low-loss electric grid an imperative, Hansen added. “This will allow dispersed renewable energies to supplant fossil fuels for power generation. Technology exists for direct-current high-voltage buried transmission lines. Trunk lines can be completed in less than a decade and expanded analogous to interstate highways,” he said.
Historically, environmental pollution problems have not been seriously addressed until they hit with full force, Hansen said. That wait-and-see approach will not work in the case of CO2 emissions and climate change because of inertial effects, warming already in the pipeline, the effect of various feedback mechanisms, and the danger of reaching the tipping point. On the contrary, ignoring emissions would lock in catastrophic climatic change, he said.
“If we go over the edge, we will transition to an environment far outside the range that has been experienced by humanity, and there will be no return within any foreseeable future generation. Casualties would include more than the loss of indigenous ways of life in the Arctic and swamping of coastal cities. An intensified hydrologic cycle will produce both greater floods and greater droughts. In the U.S., the semiarid states from central Texas through Oklahoma and both Dakotas would become more drought-prone and ill-suited for agriculture, people, and current wildlife. Africa would see a great expansion of dry areas, particularly southern Africa. Large populations in Asia and South America would lose their primary dry season freshwater source as glaciers disappear. A major casualty in all this will be wildlife,” Hansen said.
-- Steve Watson, CASMGS Communications
-- Linda Madl, CASMGS Communications