Anthropogenic Global Warming Debate Presentation
Question What causes global warming?
Science of Global Warming: Why the Climate Changes: Emissions of Heat-Trapping Gases and Aerosols
Question Who says humans are causing global warming?
"The scientific understanding of
climate change is now sufficiently clear to justify nations taking prompt
action."
-Joint [11] Science Academies’
Statement: Global Response to Climate Change, 2005
"Greenhouse gases are accumulating
in Earth’s atmosphere as a result of human activities, causing surface air
temperatures and subsurface ocean temperatures to rise."
-Climate Change Science, U.S.
National Academy of Sciences, 2001
Question But how do these guys know humans are causing global warming?
Excerpt Global climate varies over time in response to climate forcings—physical factors external to the climate system that force a net increase (positive forcing) or net decrease (negative forcing) of heat in the climate system as a whole (Hansen, Sato et al. 2005). This type of change is distinct from internal climate variability, in which heat is transported by winds or ocean currents between different components of the climate system with no net change in the total heat within the system. Because the observed climate change over the twentieth century results from a net increase of heat in the entire climate system, it can only be explained by external forcing (Hansen, Nazarenko et al. 2005). Hence, the task for climate change scientists is to identify one or more external forcing(s)—natural or man made—that can explain the observed warming.
Earth's Energy Imbalance: Confirmation and Implications
Excerpt 2 Fingerprint matching between climate forcings and observed climate change is performed using physical climate models that calculate how each forcing should have affected climate over time, based on its history and how scientists understand the physical mechanisms of each forcing. These models are able to reproduce most of the major features of the global climate system, including the pattern of global warming over the past century (e.g., Stott et al. 2000).
External Control of 20th Century Temperature by Natural and Anthropogenic Forcings
Excerpt 3 The twentieth-century warming trend at the earth’s surface progressed in a distinct pattern, with a large warming during 1910-1940, moderate cooling during 1940-1975, and a large warming from 1975 to the present (Fig. 1). Scientists at the National Center for Atmospheric Research (NCAR) looked for fingerprints of various natural (solar radiation, volcanic particles) and man-made (greenhouse gases, sulfate aerosols) forcings in this record of observed climate change (Meehl et al. 2004). The study employed a physical climate model that allowed individual or combinations of forcings to drive the simulated climate. The change in surface temperature calculated by the model for each forcing or combination of forcings was then compared with the observed record of surface temperature change over the twentieth century (Fig. 4). The best fit of the model results to the observed climate was produced when all of the forcings were included, implicating all of the forcings in producing the overall pattern of change (Fig. 4A). However, different forcings dominated at different times during the century (Takemura et al. 2006). For instance, the temperature rise in the early part of the century was dominated by natural forcings (Fig. 4B), whereas the warming after 1975 was dominated by man-made greenhouse gases (Fig. 4C). The cooling during the mid-century was consistent with a combination of natural volcanic and man-made aerosols (Nagashima et al. 2006).
The results of this study implicate the enhanced greenhouse effect as the dominant cause of global warming over the past three decades. If not for the temporary cooling between 1940 and 1975 from volcanic and man-made aerosol emissions, the earth might be even warmer than it is today (Mitchell et al. 2001).
Combinations of natural and anthropogenic forcings in the 20th century climate
Effect of carbonaceous aerosols on surface temperature in the mid twentieth century
Interject The previous excepts just cover models from a couple systems. There are other systems, such as ocean temperature and troposphere height, that through fingerprinting show the signs of human caused enhanced global warming. All forcings which effect climate are used in these models, including sun spots, solar flares, and volcanic activity.
Penetration of Human-Induced Warming into the World's Oceans
A Stellar View on Solar Variations and Climate
The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature
Excerpt 4 Independent modeling of different components of the climate system demonstrates that man-made greenhouse gases have been the dominant forcing of climate change over the past halfcentury. The distinct fingerprint of man-made greenhouse gases has been detected in records of surface temperature, ocean heat content, and the vertical structure of the atmosphere above the earth’s surface.
Excerpt 5 Scientific understanding of the causes of climate change has progressed dramatically in the past few years. Natural internal variability is an inherent feature of the climate system, but it cannot account for the net gain of energy that has been detected within the climate system as a whole. Based on physical principles, the modern increase in the heat content of the global ocean demonstrates that positive external forcing of the climate is underway. Changes in natural external forcings cannot explain the observed global warming of recent decades Records of observed climate change at the earth’s surface, in the global ocean, and in the atmosphere, bear the fingerprint of the enhanced greenhouse effect, which is caused by human activities associated with fossil fuel burning and land use.
Question Don’t natural sources like volcanoes cause global warming as well?
Excerpt Volcanic eruptions can enhance global warming by adding CO2 to the atmosphere. However, a far greater amount of CO2 is contributed to the atmosphere by human activities each year than by volcanic eruptions. Volcanoes contribute about 110 million tons/year, whereas other sources contribute about 10 billion tons/year. The small amount of global warming caused by eruption-generated greenhouse gases is offset by the far greater amount of global cooling caused by eruption-generated particles in the stratosphere (the haze effect). Greenhouse warming of the earth has been particularly evident since 1980. Without the cooling influence of such eruptions as El Chichon (1982) and Mt. Pinatubo (1991), described below, greenhouse warming would have been more pronounced.