Technical Resources

Agriculture and Climate Change

RCA Issue Brief #3
October 1995

What is the greenhouse effect, and what do we mean by climate change?
What could happen to agriculture?
What in the world are we doing about it?
What is the American contribution?
How can agriculture help?
Do we know enough?
What are the benefits of taking action now?

Did you know ...

...that by sequestering carbon, agriculture helps to offset greenhouse gas emissions? That rangeland and deep-rooted perennial crops help keep carbon dioxide, the principal greenhouse gas, from the atmosphere? But that agriculture also emits greenhouse gases, mostly methane from cattle, but also nitrogen oxide from fertilizer and emissions from fossil fuel use?

...that windbreaks to reduce erosion also can help sequester carbon--and when they shelter buildings, reduce energy consumption and the greenhouse gases produced by burning fossil fuels?

...that minimum till, no-till, and other conservation practices in agriculture reduce greenhouse gas emissions by lowering use of machinery and the emissions from fuel burned? And that by enhancing organic materials in soil, these practices increase soil's ability to sequester carbon?

...that in ruminating and digesting, cattle give off methane? And that this can be reduced by changes in diet and quality of food?

What is the greenhouse effect, and what do we mean by climate change?

Certain gases such as carbon dioxide, methane, and nitrous oxide act in the atmosphere much as the glass in a greenhouse, trapping heat from sunlight near the earth's surface. In the proper balance and occurring naturally, these atmospheric gases are essential to life on Earth. Climate change--long-term fluctuations in temperature, precipitation, wind, and all other aspects of the Earth's climate--has been a natural phenomenon over the millennia, induced by such events as volcanic eruptions, ice ages, and changes in forest cover and ocean currents and temperature. Estimates are that without naturally occurring greenhouse gases, the Earth's temperature would be 60 degrees (Fahrenheit) cooler than it is today; during the last ice age the temperature was 9 degrees cooler than current temperatures. With the advent of the industrial revolution, large quantities of carbon dioxide and other greenhouse gases began to be introduced into the earth's atmosphere. The result may well be climate change, this time because of human activity.

What could happen to agriculture?

If climate changes and temperatures rise, there are a number of potential effects. The timing and length of growing seasons might shift geographically, which would alter planting and harvesting dates and likely result in a need to change crop varieties currently used in a particular area. Seasonal precipitation patterns and amounts could change. With warmer temperatures, evapotranspiration rates would rise, which would call for much greater efficiency of water use. Weed and insect pest ranges could shift. Perhaps most important of all, there is general agreement that in addition to changing climate, there would likely be increased variability in weather, which might mean more frequent extreme events such as heat waves, droughts, and floods.

What in the world are we doing about it?

The likelihood and potential impacts of climate change have been the subject of intense concern and debate over the past decade. One result of this discussion was the signing of the Framework Convention on Climate Change (FCCC) at the Earth Summit in Rio de Janeiro, Brazil, in June 1992. The United States is a signatory to that Convention, which the U.S. Senate ratified in 1993. In signing the FCCC, the developed nations pledged to "take the lead in combating climate change and the adverse effects thereof." To this end, the United States and other countries pledged to seek to reduce their emissions of greenhouse gases to their 1990 levels by the year 2000.

What is the American contribution?

The United States generates about 20 percent of the total global greenhouse gases emitted annually. Of this U.S. share, American agriculture generates a relatively small portion: 1.8 percent of the carbon dioxide, 14 percent of the methane, and 7.5 percent of the nitrous oxide. Agricultural emissions of carbon dioxide come from fertilizer and pesticide manufacture, field machinery use, transportation, irrigation, livestock production, and crop drying. Globally, methane emissions come from rice paddies (28 percent), ruminant animals (20 percent), wetlands (11 percent), and other sources (6 percent). Most methane emissions from agriculture in the United States come from livestock. Nitrogen oxide in agriculture is emitted primarily by nitrogen fertilizers which, once applied, break down in the soil and can become airborne in their gaseous forms.

How can agriculture help?

A number of measures exist that agriculture can take both to increase the quantity of carbon it sequesters (captures) and to reduce its share of greenhouse gas emissions:

increase conservation tillage and other crop residue management practices to lower emissions from equipment and increase soil organic-matter content;
use low-greenhouse gas fuels, such as diesel and alcohol-based fuels from biomass (woody and herbaceous plant tissue and animal wastes that can be converted to energy);
better manage cattle waste and, if possible, trap or process methane, or both, for its energy and nutrient content; and
apply nitrogen fertilizers only when and in quantities and forms needed by crops. This reduces emissions of the oxide.

By carefully husbanding resources and land uses that accumulate carbon (sinks)--such as lands primarily in perennial crops and forest--and by changing the practices to avoid generating greenhouse gases, agriculture can make an important contribution to meeting the goals of the Climate Change Convention.

Do we know enough?

We lack specific knowledge about the nature and effects of current climate change trends (and there are still many uncertainties and disagreements). We also need to know more about the actual capacity of agriculture to sequester carbon. Initiatives are being taken by USDA and others to assess, with greater precision than has been done up to now, the nature and extent of carbon sequestration in soil, in the diverse crop systems, and in the many microclimates found in the United States.

What are the benefits of taking action now?

The beauty of "doing something" now about climate change is that almost any action taken helps to solve other problems. Retaining ground cover for the purpose of storing carbon also can:

reduce or prevent erosion;
restore damaged land and water resources;
reduce local air pollution;
reduce water pollution by reducing runoff;
enhance wildlife habitat and biodiversity; and
increase production of biomass and other alternative crops.

Changing tillage practices, preserving crop residues, and similar measures can:

reduce the need for fertilizer inputs that are energy-intensive in their manufacture and application (both of which can produce local pollution and require the use of fossil energy, much of it imported) and also save money;
decrease emissions of oxides of nitrogen by applying nitrogen fertilizers only when and in quantities needed;
decrease the costs of chemical and mechanical treatments of crops and the labor they require;
reduce field activity with equipment, thereby reducing farm emissions from fossil fuels; and
recognize animal wastes as a resource, rather than a burden, by using them for energy to supplant other forms of energy, and by using them for fertilizer to substitute for commercial nutrient sources.

Likewise, "doing something" about other environmental problems associated with agriculture--erosion, air pollution, water pollution, animal waste, energy efficiency, and alternative energy sources--can help meet the nation's obligations regarding greenhouse gases and climate change.

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