Question:

Is human activity a substantial cause of global climate change?

Critical thinkers look more closely at the quality of arguments than the quantity.

Background Information:

The US National Academies of Science, the National Aeronautics and Space Administration (NASA), and the National Oceanic and Atmospheric Administration (NOAA), and many others, say that greenhouse gas levels are rising due to human activities such as burning fossil fuels and deforestation (cutting down the forests) which are causing significant climate changes including global warming, loss of sea ice, glacier retreat, more intense heat waves, stronger hurricanes, and more droughts. They say that climate change requires immediate international action to prevent dire consequences.

The argument is that human-generated greenhouse gas emissions are too small to substantially change the earth’s climate. They state that our forests and oceans are capable of absorbing these small increases, and that 20th century warming has resulted from natural processes including changes in the sun's heat and ocean currents. They say that global climate change is based on nonsense science and scare tactics.

Human activities release greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (NO2), into the atmosphere. As of Apr. 2010, CO2 levels were reportedly higher than at any time in the last 650,000 years. This rise took place alongside a 20th century global temperature increase of between 1°F and 1.4°F.
Many researchers think the earth will continue to warm by 3-10°F over the 21st century.
Predictions about how climate changes will affect civilization range from Department of Defense report detailing catastrophic weather events to an increasingly lush environment of plants and animals.

Carbon dioxide (CO2) is released and absorbed in the global carbon cycle.
Source: United States Department of Energy "Simplified Global Carbon Cycle," (accessed June 2, 2010)

Scientists have know of the heating potential (greenhouse effect) of gases such as CO2 since at least Jan. of 1859, when British physicist John Tyndall first began experiments leading to the discovery that CO2 in the atmosphere absorbs the suns heat.

On Feb. 16, 1938, engineer Guy S. Callender published a study suggesting increased atmospheric CO2 from fossil fuel combustion was causing global warming. Many scientists criticized the study arguing that CO2 had a negligible effect on temperature compared to water vapor and atmospheric circulation changes.
In March 1958, US climate scientist Charles Keeling began measuring atmospheric CO2 at the Mauna Loa observatory in Hawaii for use in climate modeling. Using these measurements, Keeling became the first scientist to confirm that atmospheric CO2 levels were rising rather than being fully absorbed by forests and oceans (carbon sinks).

In 1977, the US National Academy of Sciences issued the report "Energy and Climate",concluding that the burning of fossil fuels was increasing atmospheric CO2, and that increased CO2 was associated with a rise in global temperatures.
On June 23, 1988, National Aeronautics and Space Administration (NASA) scientist James Hansen presented testimony to the US Senate stating directly that increases in CO2 were warming the planet and "changing our climate." The testimony was based on Hansen and colleagues' Aug. 1988 peer-reviewed study on Global Climate Change. Many scientists, including MIT Meteorologist Richard Lindzen, criticized Hansen's findings arguing that his climate models were unreliable, and that negative feedback loops would balance out any warming caused by increased CO2.

Also in 1988, the Intergovernmental Panel on Climate Change (IPCC) was created by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to review research on global climate change. The IPCC issued its first assessment report in 1990 stating that "emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases," resulting in "an additional warming of the Earth's surface."

Arctic ice cap from 1979 (red line) to 2005 - a 20% retreat.
Source: Natural Resources Defense Council, "Global Warming Puts the Arctic on Thin Ice," (accessed June 2, 2010)

On Oct. 13, 1992, US President George Bush signed the United Nations Framework Convention on Climate Change. The goal of the convention was the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system."

In Dec. 1997, over 161 nations met in Kyoto, Japan, to negotiate a treaty to limit greenhouse gas emissions and work toward the objectives of the UNFCCC. The resulting Kyoto Protocol set binding targets for 37 industrialized countries and the European Union to reduce greenhouse gas emissions roughly 5% below 1990 levels by 2012.

In 2006, Al Gore's documentary An Inconvenient Truth premiered and was seen by over 5 million worldwide. The film argued that human caused climate change was real, and that without immediate reductions in greenhouse gas emissions, catastrophic climate changes would severely disrupt human societies, leading to a possible collapse of industrial civilization.

In 2007, the IPCC released its fourth assessment report stating that "warming of the climate system is unequivocal" and that "most of the observed increase in global average temperatures since the mid-20th century is very likely [90% confidence] due to the observed increase in anthropogenic [man-made] greenhouse gas concentrations." The IPCC and Al Gore received a Noble Peace Prize for their climate science work in Oct. 2007.

In response to the IPCC findings, a group of scientists formed the Nongovernmental International Panel on Climate Change (NIPCC) to compile a report challenging the science behind man-made climate change. The Mar. 2, 2008 report, "Nature, Not Human Activity, Rules the Climate", was published by the Heartland Institute. On Mar. 2-4, 2008, Heartland held its first international conference attended by over 400 scientists, economists, and other experts questioning human-caused global warming. At the conference, 98 speakers, including PhD climate scientists from major universities, argued that global warming was most likely a natural event.

Graph showing that rising CO2 levels correlate with higher global temperatures.
Source: National Oceanic and Atmospheric Administration, "Global Climate Change Indicators," (accessed Apr. 13, 2010)

On Dec. 7, 2009, the US EPA announced their findings on greenhouse gases determining that they "threaten public health" and are "the primary driver of climate change." This statement was in response to the US Supreme Court ruling (5-4) in Massachusetts v. EPA that greenhouse gases met the criteria to be considered pollutants under the Clean Air Act.

In Dec. 2009 the COP 15 conference took place in Copenhagen, Denmark. The Copenhagen Accord, created by the US, China, India, Brazil, and South Africa, called for a rise of no more than 2°C, to be achieved by "deep cuts in global emissions" of greenhouse gases.


(Click to enlarge image)
Graph showing that Arctic air temperature (blue line) parallels natural solar activity (red line).
Source: Oregon Institute of Science and Medicine, "Environmental Effects of Increased Atmospheric Carbon Dioxide," Journal of American Physicians and Surgeons, Fall 2007

From 1998-2009, the US government appropriated $99 billion for work related to climate change. $35.7 billion (36%) of that total came in 2009 as part of the American Recovery and Reinvestment Act of 2009.

In Apr. 2010, Bolivia hosted an alternative to the UN COP conferences. The World People's Conference on Climate Change and the Rights of Mother Earth was attended by representatives from nearly 130 countries. The People's Agreement reached at the conference demanded that developed countries lower CO2 levels back to 300 ppm (from 389ppm), and rejected the Copenhagen Accord for its "insufficient reductions in greenhouse gases." It stated that "[c]limate change is now producing profound impacts on agriculture and the ways of life of indigenous peoples and farmers throughout the world."

As of 2010, the US had 4.5% of the world's population but was responsible for about 28% of all global greenhouse gas emissions.

PRO Human activity is causing global climate change.

  1. 75% of the 20th century increase in the atmospheric greenhouse gas CO2 is directly caused by human actions like burning fossil fuels. CO2 levels were 389ppm (parts per million) as of Apr. 2010 - the highest they have been in the past 650,000 years.This increase in CO2 was a substantial contributor to the 1°F to 1.4°F warming over the 20th century.
  2. Human-produced CO2 is warming the earth, not natural CO2 released from the ocean and other "carbon sinks." CO2 from fossil fuel combustion has a specific isotopic ratiothat is different from CO2 released by natural "carbon sinks." 20th century measurements of CO2 isotope ratios in the atmosphere confirm that the rise results from human activities, not natural processes.
  3. Human produced greenhouse gases will continue to accumulate in the atmosphere causing climate change because the earth's forests, oceans, and other "carbon sinks" cannot adequately absorb them all. As of 2009, these carbon sinks were only absorbing about 50% of human-produced CO2. The other 50% is accumulating in the atmosphere.
  4. Human greenhouse gas emissions, not changes in the sun's radiation, are causing global climate change. Measurements in the upper atmosphere from 1979 - 2009, show the sun's energy has gone up and down in cycles, with no net increase. While warming is occurring in the troposphere (lower atmosphere), the stratosphere (upper atmosphere) is cooling. If the sun was driving the temperature change there would be warming in the stratosphere also, not cooling.
  5. Computer models show that increased levels of human produced greenhouse gases will cause global warming and other climate changes. Although these climate models are uncertain about how much future warming will occur and how it will affect the climate, they all agree that, to some degree, these changes will happen. The reality of climate change is not contradicted by this uncertainty.
  6. Although the amount of human-produced greenhouse gases may seem small to some people, their warming potential is amplified by the water vapor positive feedback loop, allowing them to cause significant warming and climate change. As greenhouse gases heat the planet, increased humidity (water vapor in the atmosphere) results. Since water vapor is itself a greenhouse gas, it can double the warming effect of greenhouse gases such as CO2.
  7. Human greenhouse gas emissions are heating the planet, and climate models consistently show that this warming causes an increase in the frequency and intensity of tropical cyclones. The fact that 1975-1989 had 171 category 4 and 5 hurricanes while 1990-2004 had 269 of them (a 57% increase) validates these climate models and the reality of human-induced climate change.
  8. Human-produced CO2 is changing the climate of the world's oceans. As excess CO2 is absorbed, oceanic acidity levels increase. Oceans have absorbed 48% of the total CO2 released by human activities and acidity levels are 25-30% higherthan prior to human fossil fuel use.
  9. An 8" rise in the ocean level has occured (1961-2003) due to human-induced global warming. Global sea levels rose an average of 1.8 mm (.07 in) per year between 1961 and 2003 and at an average rate of about 3.1 mm (.1 in) per year from 1993 to 2003. This sea level rise is the result of warming waters and the melting of glaciers, ice caps, and polar ice sheets. From 1870-2004, a "significant acceleration" of sea-level rise occured, an important confirmation of climate change models.
  10. Warming caused by human-produced greenhouse gases is changing the earth's hydrologic climate. Rainfall is increasing in many areas due to increased evaporation stemming from global warming. Higher temperatures are also causing some mountainous areas to receive rain rather than snow. According to researchers at the Scripps Institution of Oceanography, up to 60% of the changes in river flow, winter air temperature, and snow pack in the western US (1950-1999) were human-induced.
  11. Warming caused by human-produced greenhouse gases is changing the rate of glacial melt and altering the local climate of many regions. Since 1850, records show a "strong increase" in the rate of glacial retreat. From 1961-2004 glaciers retreated about .5mm per year in sea level equivalent. According to the World Glacier Monitoring Service, since 1980, glaciers worldwide have lost nearly 40 feet (12 meters) in average thickness (measured in average mass balance in water equivalent).
  12. Warming caused by human-produced greenhouse gases and soot (black carbon) produced from burning of fossil fuels and deforestation, is reducing the size of the Arctic ice cap. A smaller ice cap reflects less of the sun's energy away from the earth. This energy is absorbed instead, causing air and water temperatures to rise. From 1953–2006, Arctic sea ice declined 7.8% per decade. Between 1979 and 2006, the decline was 9.1% each decade. Climate models predict that Arctic sea ice will continue to retreat through the 21st century further disrupting the global climate.
  13. Many organization believe that human activity is a substantial cause of global climate change. These groups include: the World Meteorological Organization (WMO), the Intergovernmental Panel on Climate Change (IPCC), the InterAcademy Council, the Network of African Science Academies, the European Science Foundation (ESF), the European Space Agency (ESA), the Royal Society (UK national academy of science), the US National Academies of Science, the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the US Environmental Protection Agency (EPA).
  14. Nearly all climate change studies show humans as the main cause, and studies which contradict this claim are often funded by petroleum companies, making their conclusions suspect given the obvious conflict of interest. From 2004-2005, ExxonMobil gave $2.2 million in grants for climate change research to organizations that deny human caused climate change. In 2006 US Senators Olympia Snowe (R-ME), and Jay Rockefeller (D-WV) chastised ExxonMobil for providing more than $19 million in funding to over 29 "climate change denial front groups."

CON Human activity is not the main cause for climate change.

  1. The 20th century warming of 1-1.4°F is within the +/- 5°F range of the past 3,000 years. A 2003 study by researchers at the Harvard-Smithsonian Center for Astrophysics shows temperatures from 1000-1100 AD (before fossil fuel use) that are comparable to those from 1900-1990.
  2. Rising CO2 levels are a result of global warming, not a cause of it. As temperatures increase, CO2 is released from "carbon sinks" such as the oceans or the Arctic tundra. Measurements of ice core samples show that over the last four climactic cycles (past 240,000 years) periods of global warming preceded global increases in CO2.
  3. Human releases of CO2 cannot cause climate change as any increases in CO2 are eventually balanced by nature. CO2 gets absorbed by oceans, forests, and other "carbon sinks" that increase their biological activity to absorb excess CO2 from the atmosphere. 50% of the CO2 released by the burning of fossil fuels and other human activities, has already been absorbed.
  4. Global warming and cooling are caused by fluctuations in the sun's heat (solar forcing), not by the minor greenhouse effect of human-produced gases such as CO2 and methane (CH4). Between 1900 and 2000 solar irradiance increased .19%. This increase correlates with the rise in surface temperatures in the US.
  5. Due to the inherent unpredictability of climate systems it is impossible to accurately use models to determine future weather. Climate models have been unable to simulate major known features of past climate such as the ice ages or the very warm climates of the Miocene, Eocene, and Cretaceous periods. If models cannot replicate past climate changes they should not be trusted to predict future climate changes.
  6. Rising temperatures are caused primarily by water vapor, the most abundant greenhouse gas in the atmosphere, not by CO2. Water vapor concentrations in the atmosphere are driven by natural storm systems and ocean currents. According to a Mar. 5, 2010 study by researchers at NOAA, water vapor in the stratosphere was responsible for increasing the rate of warming during the 1990s by 30%.
  7. The increased hurricane activity over the past decade (1995-2005), including hurricane Katrina, is not the result of human-induced climate change; it is the result of cyclical tropical cyclone patterns, driven primarily by natural ocean currents, according to the National Oceanic and Atmospheric Administration's (NOAA) testimony in the US Senate on Sep. 20, 2005.
  8. Deep ocean currents cause climate warming and cooling in long term cycles. The minor greenhouse effect of human produced CO2 pales in comparison. Global cooling from 1940 to the 1970s, and warming from the 1970s to 2008, coincided with fluctuations in ocean currents and cloud cover driven by the Pacific Decadal Oscillation (PDO) - a naturally occuring rearrangement in atmospheric and oceanic circulation patterns.
  9. Ocean acidity levels have risen over the 20th century, but they are not out of the ordinary considering the fluctuations of the past 7,000 years. Average ocean surface water pH is 8.1 and has only decreased 0.1 since the beginning of the industrial revolution (neutral is pH 7, acid is below pH7).
  10. Changes in ocean currents are primarily responsible for the melting Greenland ice sheet, Arctic sea ice, and Arctic permafrost. Over the 20th century there have been two Arctic warming periods with a cooling period (1940-1970) in between. According to a peer-reviewed Apr. 19, 2009 study in Geophysical Research Letters, natural shifts in the ocean currents are the major cause of these climate changes, not human generated greenhouse gases.
  11. The general consensus that the earth has warmed during the 20th century is based upon flawed temperature measurements. These measurements, taken from surface monitoring stations set up by the National Weather Service (NWS), are often contaminated by the "heat island effect." According to a Mar. 2009 study published by the Heartland Institute, 89% of NWS monitoring stations are too close to artificial heat sources such as large asphalt parking lots, air conditioners, heaters and other sources of artificial heat.
  12. Many organizations believe that nature, not human activity, is primarily responsible for climate change. These groups include: the Heartland Institute, the Heritage Foundation, the Competitive Enterprise Institute, the George C. Marshall Institute, the CATO Institute, the American Enterprise Institute, the Institute for Energy Research, the NationalCenter for Policy Analysis, the American Association of Petroleum Geologists, and the Oregon Institute of Science and Medicine.
  13. Theories of naturally caused climate change are often ignored by "mainstream" scientists and organizations because many research scientists are more interested in maintainining the flow of federal grant money for climate change research than in questioning the basic theory of human causation. From 1998-2009, nearly $25 billion in federal funds was allocated for climate science research. Researchers who question human-induced climate change often do not receive grant money for research projects.

Background: "Is human activity a substantial cause of global climate change?"