Events & Media

Straight Talk on CO2 and Climate Change
A short interview with Zurich Financial Services Distinguished Visitor on Climate Change Don Wuebbles


Don Wuebbles

Note: The following interview was conducted by the media office at the University of Illinois, Urbana-Champaign (UIUC), Dr. Wuebbles' home institution. He spoke at the Bren School on May 15 (the tape of his talk will be available on the Bren School YouTube page soon) and is currently teaching a short course based on the US National Climate Assessment, for which he served as a lead author. (Read his biography)

May 15, 2013

UIUC: Carbon dioxide (CO2) has passed 400 parts per million (ppm) in the atmosphere. What does that mean (both in definition and implication)?

DW: Last Thursday, global atmospheric concentrations of carbon dioxide, as measured at Hawaii's Mauna Loa Observatory, reached 400 parts per million (ppm) for the first time since accurate measurements of CO2 started there in 1958. The location of Mauna Loa is such that it is close to the global averaged concentration of CO2. Before the Industrial Revolution, natural levels of carbon dioxide in the atmosphere averaged around 280 parts per million (ppm). In other words, carbon dioxide made up about 0.028% of the volume of the atmosphere. Over the last few centuries, emissions from human activities, especially the burning of fossil fuels like coal and oil, along with changes in land use, have increased the atmospheric concentration of carbon dioxide to the current level.

Despite being such a small portion of the atmosphere, carbon dioxide and other heat-trapping gases (also called greenhouse gases) are extremely important to the Earth’s climate. Without these gases, this would be a frozen planet. The reason why heat-trapping gases like CO2 have such an influence on the Earth’s climate is that they are largely transparent to the visible and ultraviolet energy emitted by the Sun but are very strong absorbers of the infrared heat energy emitted from the Earth’s surface. Water vapor is the most important naturally occurring heat-trapping greenhouse gas, but the amount of water vapor in the atmosphere tends to increase as the atmosphere warms – as a result, water vapor is considered a “feedback” rather than a direct forcing on climate.

Increases in atmospheric levels of heat-trapping gases like carbon dioxide enable these gases to absorb ever-increasing amounts of infrared heat energy. The gases absorb the infrared energy emitted from the Earth’s surface and then radiate some of this heat back to the surface, effectively trapping the heat inside the Earth’s climate system and warming the Earth’s surface.

The problem is that the concentration of CO2 will not stop at 400 ppm but will continue to increase as a result of human emissions, at least until we greatly decrease those emissions. The atmospheric lifetime of CO2 is very long so we are committing future generations to higher levels of CO2 and a different climate than we have seen in the past.

UIUC: What makes this a milestone? Can you put it in historical perspective for us?

DW: The last time the Earth has seen CO2 levels as high as 400 ppm was over 2 million years ago, during the Pliocene (approximately 2.6 to 5.3 million years ago). Recent estimates suggest CO2 levels reached as much as 415 parts per million (ppm) during the Pliocene – we will likely pass that level in the next decade (the difference is how rapidly we are currently increasing the levels of CO2). With that level of CO2 came global average temperatures that eventually reached 5 to 7 degrees F higher than today’s during the mid-Pliocene and as much as 18 degrees F warmer at the poles. Sea level ranged between 15 to 130 feet higher than today. A paper in the journal Science published just this week discusses the much warmer polar regions during the Pliocene compared to today. The large heat capacity of the oceans will keep us from reaching such effects quickly, especially in terms of sea level rise, but the problem is that CO2 levels are still rising and could reach 500-800 ppm or more before the end of this century unless we greatly slow down the rate of increase.

UIUC: What can be done to reduce the carbon dioxide in the atmosphere? Or are we too late?

DW: There are multiple paths forward in response to climate change. One choice is do nothing and try to deal with the consequences. However, a number of economic analyses have concluded that the costs from inaction would be much larger than the costs of action. Another choice is to significantly reduce the emissions of heat-trapping gases by changing the way that we use energy and transportation systems. Through using energy and transportation more efficiently and by switching to alternative sources of energy that reduce or eliminate the emissions of carbon dioxide (and other heat-trapping gases and particles), we can significant limit the effects on climate over the coming decades.

Increased efficiency in energy use is important, as is the increased use of energy technologies that do not produce carbon dioxide. For example, because about 28% of the energy used in the U.S. is used for transportation, changing the types of fuel that we use to those that do not contribute significantly to heat-trapping gas emissions (such as biofuels if their production is not dependent on fossil fuels and does result in other environmental effects) and driving more efficient vehicles is one obvious path forward. A large amount of energy in the U.S. is also used to heat and cool buildings, so changes in building design could dramatically reduce energy use. There are many pathways that can help prevent the largest of the potential impacts on humanity and ecosystems from climate change.

UIUC: What implications does this milestone have for policy?

DW:Like the first explorers, we are entering uncharted territory – there has never been this much atmospheric CO2 in the human experience. This milestone is another indicator of the urgency for policies to be implemented to reduce human-related emissions of carbon dioxide, as well as those of other heat-trapping gases like methane and nitrous oxide. Policies are needed that will prevent the worst of the changes in climate that will otherwise occur. Some further changes in climate are inevitable, but we can limit the impacts and prevent the largest changes in temperature and in severe weather that are likely without such actions.

Adaptation will also be necessary. Because impacts from the changing climate are already occurring and anticipated to increase at least in the short term, adaptation to the impacts of climate change will be required. Adaptation decisions range from being better prepared for extreme events such as floods and droughts, to identifying economic opportunities that come from investments in adaptation and mitigation strategies and technologies, to integrating considerations of new climate-related risks into city planning, public health and emergency preparedness, and ecosystem management.