Climate lag is defined as a delay that can occur in a change of some aspect of climate due to the influence of a factor (s) that is slow-acting. An example of climate lag is the full effect of the release of a particular amount of carbon dioxide into the atmosphere. Following its release, some of the gas is absorbed by ocean water to be released into the atmosphere later on as part of the global carbon cycle. Thus, the full effect of carbon dioxide on the warming of the atmosphere will not be apparent until the ocean-bound gas has been released.
Climate lag is an important concept in climate modeling, and in forming policies to deal with climate change. The climate change that is apparent at a certain point in time may not be an accurate indication of the eventual change. Basing an emissions reduction strategy on current data may not completely address the problem.
Historical Background and Scientific Foundations
Climate lag is a function of scale. The volume of water in the ocean is huge—over 322 million cubic mi (1.34 billion cubic km). As a result, changes in the ocean chemistry will occur slowly and will be apparent as only slight changes. An example is the pH of the ocean (pH is a measure of the quantity of acidic and basic compounds). Measurements done throughout the twentieth century have revealed a pH decrease in the ocean. Although the decrease is slight, this means that the ocean is becoming more acidic. The scientific agreement is that this is due to the absorption of atmospheric carbon dioxide by the water.
Because elements such as carbon dioxide cycle between the land, water, and air on a global scale, the carbon dioxide in the ocean will ultimately cycle into the atmosphere. Although not all scientists agree, the majority of climate scientists view the changing ocean pH as a consequence of climate lag. As carbon dioxide has accumulated in the atmosphere, its increased absorption by the ocean has followed. According to an article published in the journal Science in 2004, almost half of the carbon dioxide produced by human-related activities in the past two centuries has been absorbed by the ocean. In the future, this carbon dioxide will be liberated from the ocean, providing a long-term source of the greenhouse gas.
Similarly, there is a climate lag with respect to ocean temperature. The rising atmospheric temperature does not immediately produce warming of the ocean. The vast volume of ocean water requires centuries to warm even a few degrees.
Impacts and Issues
Climate lag has important implications for efforts to slow the warming of Earth's atmosphere. Because carbon dioxide is absorbed by ocean waters and slowly released to the atmosphere, there will continue to be a source of the greenhouse gas even if the release of carbon dioxide by human-related industrial and other activities were to stop.
Scientists at the U.S. National Center for Atmospheric Research have modeled the contribution of ocean-bound carbon dioxide to global warming. They determined that even if greenhouse gas production remained constant, the temperature of the atmosphere will continue to rise for another 100 to 200 years. As well, continued melting of polar ice over the next several centuries will continue to drive an increase in sea level.
WORDS TO KNOW
CARBON CYCLE: All parts (reservoirs) and fluxes of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of Earth, but most of that pool is not involved with rapid exchange with the atmosphere.
CLIMATE MODEL: A quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive.
GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.
KYOTO PROTOCOL: Extension in 1997 of the 1992 United Nations Framework Convention on Climate Change (UNFCCC), an international treaty signed by almost all countries with the goal of mitigating climate change. The United States, as of early 2008, was the only industrialized country to have not ratified the Kyoto Protocol, which is due to be replaced by an improved and updated agreement starting in 2012.
Some critics of the Kyoto Protocol have used climate lag to argue that the emission targets are not nearly stringent enough to achieve the desired climate change, since the reduction in produced greenhouse gases will be small in comparison to the gases still to be released from the ocean. Others invoke climate lag to argue against the protocol for the opposite reason, claiming that to realistically deal with greenhouse-gas production, the emission reduction targets would have to be so great as to be unachievable. The latter view was part of Canada's withdrawal of support for the Kyoto Protocol in 2007.
DiMento, Joseph F.C., and Pamela M. Doughman. Climate Change: What It Means for Us, Our Children, and Our Grandchildren. Boston: MIT Press, 2007.
Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. New York: Rodale Books, 2006.
Seinfeld, John H., and Spyros N. Pandis. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. New York: Wiley Interscience, 2006.
Feely, R. A., C. L. Sabine, K. Lee, et al. “Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans.” Science 305 (2004): 362-366.