IPCC
To understand the very best projections for future climate change, we need to understand the workings of the IPCC, the Intergovernmental Panel on Climate Change. The IPCC was founded in 1988 by the World Meteorological Society (WMO) and the United Nations Environmental Program (UNEP) to summarize and assess climate change science and related peer-reviewed studies from thousands of researchers around the world. It has published reports of such summaries and assessments in 1990, 1995, 2001, 2007, and 2013-2014. With the evolution of the research and increased observations, the IPCC assessments have become more sure about their conclusions. In 1995, the report concluded that present climate change was caused by human activities “more likely than not.” In 2001, the conclusion was “likely.” In 2007, “very likely.” And in 2013, “extremely likely.” This is because only in the late 1990s and early 2000s did global warming emerge as a trend from the “background noise” of natural climate variability caused by other factors. The IPCC’s findings have been endorsed by nearly two hundred scientific agencies around the world, and have been supported by independent reviews of the scientific literature.
IPCC reports include summaries of thousands of scientific studies and millions of observations, projected impacts, the potentials for mitigation, and summaries for policy makers. A given report may be over 800 pages, and may have 120 authors, 500 contributors, and 700 collaborators. In 2007, the IPCC shared the Nobel Peace Prize. Most importantly, such reports include projections of future climate change from computer models.
Models
To create their projections of likely future climate change, scientists have created elaborate computer models of the earth’s climate system, and these models have increased in number, complexity, and refinement over time. About forty different Atmosphere-Ocean General Circulation Models (AOGCMs), most of them funded by national governments, have been created by independent teams of scientists around the world. These take into account the full three-dimensional structure of the atmosphere and oceans, the continents including details of coastlines and surface topography, sea ice, vegetation, water vapor, ocean currents, and ice melting. These models also incorporate all natural variables, including solar irradiance, volcanic eruptions, unusual weather patterns, and so on. Since sulfate aerosols from power stations increase the earth’s reflectiveness, or albedo, they are also included since although they only have a lifetime of a few weeks in the atmosphere, they are continually emitted. These models are checked by “hind-casting” against historic and paleoclimate records to see if they can predict changes already observed. They could reproduce medieval warmth and the Little Ice Age variations, but not 20th century warming without figuring in human influences.
The results of simulation runs are compared for agreement and divergence. In all cases, only human impacts could reproduce observed warming. Model runs which did not include human-caused increases in greenhouse gases could not recreate the observed strong warming since the 1970s. Different models developed by different scientists with different assumptions in different places still show roughly the same upward trend in global temperatures and sea levels for the next 100 years. However, sea ice is presently disappearing faster than projected, perhaps due to factors like soot, algae, bacteria, and the dynamics of melting glaciers which are not yet well-modeled.
Presently, models have become so good that they can accurately simulate regional details of climate change, so we can better understand how each area will likely be affected differently.
To understand the very best projections for future climate change, we need to understand the workings of the IPCC, the Intergovernmental Panel on Climate Change. The IPCC was founded in 1988 by the World Meteorological Society (WMO) and the United Nations Environmental Program (UNEP) to summarize and assess climate change science and related peer-reviewed studies from thousands of researchers around the world. It has published reports of such summaries and assessments in 1990, 1995, 2001, 2007, and 2013-2014. With the evolution of the research and increased observations, the IPCC assessments have become more sure about their conclusions. In 1995, the report concluded that present climate change was caused by human activities “more likely than not.” In 2001, the conclusion was “likely.” In 2007, “very likely.” And in 2013, “extremely likely.” This is because only in the late 1990s and early 2000s did global warming emerge as a trend from the “background noise” of natural climate variability caused by other factors. The IPCC’s findings have been endorsed by nearly two hundred scientific agencies around the world, and have been supported by independent reviews of the scientific literature.
IPCC reports include summaries of thousands of scientific studies and millions of observations, projected impacts, the potentials for mitigation, and summaries for policy makers. A given report may be over 800 pages, and may have 120 authors, 500 contributors, and 700 collaborators. In 2007, the IPCC shared the Nobel Peace Prize. Most importantly, such reports include projections of future climate change from computer models.
Models
To create their projections of likely future climate change, scientists have created elaborate computer models of the earth’s climate system, and these models have increased in number, complexity, and refinement over time. About forty different Atmosphere-Ocean General Circulation Models (AOGCMs), most of them funded by national governments, have been created by independent teams of scientists around the world. These take into account the full three-dimensional structure of the atmosphere and oceans, the continents including details of coastlines and surface topography, sea ice, vegetation, water vapor, ocean currents, and ice melting. These models also incorporate all natural variables, including solar irradiance, volcanic eruptions, unusual weather patterns, and so on. Since sulfate aerosols from power stations increase the earth’s reflectiveness, or albedo, they are also included since although they only have a lifetime of a few weeks in the atmosphere, they are continually emitted. These models are checked by “hind-casting” against historic and paleoclimate records to see if they can predict changes already observed. They could reproduce medieval warmth and the Little Ice Age variations, but not 20th century warming without figuring in human influences.
The results of simulation runs are compared for agreement and divergence. In all cases, only human impacts could reproduce observed warming. Model runs which did not include human-caused increases in greenhouse gases could not recreate the observed strong warming since the 1970s. Different models developed by different scientists with different assumptions in different places still show roughly the same upward trend in global temperatures and sea levels for the next 100 years. However, sea ice is presently disappearing faster than projected, perhaps due to factors like soot, algae, bacteria, and the dynamics of melting glaciers which are not yet well-modeled.
Presently, models have become so good that they can accurately simulate regional details of climate change, so we can better understand how each area will likely be affected differently.