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Mount Rainier Mount Rainier’s glaciers. © © Lisa Feldkamp/The Nature Conservancy

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Climate Change

Frequently Asked Questions. Use this Q&A to have the best information at hand when you have conversations about climate change and its possible solutions.


Climate change is complicated and there are a lot of scientists who dispute the alarms we hear from the environmental community. Are we sure we know enough to justify all the changes to our economy now when the impacts won’t happen for decades or centuries?

Evidence: Only a very small minority of scientists dispute the basic consensus on climate change: the Earth is warming; human activities, including use of fossil fuel sources of energy, are a major cause of the warming; and, unchecked, this rapid warming presents significant risks to human communities and natural systems. In fact, we are already seeing impacts from global warming today.

There has never been more science done to understand any other environmental threat. The U.S. government has spent billions of dollars on climate science across many agencies and universities. The United Nations has assembled thousands of scientists to compile and review the latest science and contribute to the publication of five reports since 1990 that have consistently made the consensus deeper and the warnings more urgent.

Factoid: The United States is now the only nation that has announced plans to withdraw from the Paris Agreement on Climate Change; Syria and Nicaragua, the last outliers, have now joined the over 185 other signatories in pledging to reduce their emissions and develop adaptation plans.


Climate change is natural and has always been occurring. There were times when the Earth was much warmer and sea levels were much higher than they are today. Why do we need to prevent climate change if nature has gone the same way in the past?

Evidence: Yes, the climate has changed many times over Earth’s history and in the past it has been many degrees warmer and colder than it is today. However, with a handful of exceptions, most of these changes happened very gradually, allowing life on Earth time to adapt to even extreme climate conditions.

A major concern with this current episode of warming is that it is happening so rapidly that humans and nature will have insufficient time to adapt. Entire ecosystems, communities, and even countries are at great risk. Much of the human population lives in coastal areas that will be inundated by higher seas and larger storms, with property losses that will total billions of dollars in this century.

While some species may adapt to rapidly changing land, freshwater, and marine habitats (some fish move quickly in response to temperature change), others will suffer population declines, collapse and even extinctions. Humans will suffer when some ecosystems no longer provide the services (food, coastal defense, clean water, etc.) we depend on.

Factoid: Over the last 7,000 years of the current epoch, temperature has been very stable with a slight cooling trend of approximately -0.01° C/century. Over the last hundred years, temperature has increased by about 0.7° C/century, 70 times the Holocene baseline. Since 1970, temperature has increased by about 1.7° C/century, 170 times the baseline. A recent report predicts the rate of increase over the next four decades will rise to 2.5° C/century, 250 times the baseline.

Temperature isn’t the only change. The rate of carbon emissions is the highest it has been in 66 million years, the rate of ocean acidification is the highest it has been in 300 million years and the rate of reactive nitrogen (source of water pollution) being added (by humans) is the most rapid impact on the nitrogen cycle for some 2.5 billion years. In fact, all these extreme, rapid changes to the Earth have led some scientists to argue we have entered a new epoch, the Anthropocene.


The Earth has not been warming since 1998. Isn’t global warming over?

Evidence: At the time, 1998 was a record-warm year with a global average temperature that was 1.13° F greater than the 1910-2000 average.

The exceptional temperature increase in 1998 was driven by a combination of CO2 pollution and the strongest El Nino weather pattern of the 20th century. As El Nino dissipated, average annual temperatures declined, but they remained well above historic levels, with 16 of the next 17 years being the hottest in the temperature record. The 2015-16 El Nino repeated the pattern. Although not as strong as the 1998 event, in combination with the CO2 impact, temperatures in 2015 and 2016 set new records exceeding the 1910-2000 average by 1.62° and 1.67° F—significant jumps above the previous trendline.

If one focuses on the whole record and not just the last extreme year, continual warming is the clear pattern.

Factoid: Affected by El Nino, the first three months of 2016 exceeded the long-term average temperature by 2.07° F and each month had the highest temperature ever recorded for that month.


If climate change is happening, why is Antarctica gaining ice?

Evidence: It is important to make a distinction between sea ice and land ice (also known as glacial ice or when referring to the Arctic and Antarctica, ice caps or ice sheets). Climate-driven sea ice change affects local ecology (i.e., polar bears, whales, plankton and fish in the Arctic and penguins, whales, plankton and fish in Antarctica) but not sea level because sea ice is already floating (a glass of ice water filled to the rim will not overflow when the ice melts). Land ice change has less of an impact on local ecology, but is very important for global sea level because as this ice melts it adds water to the oceans.

Climate change is driving more rapid temperature increases on land than in the oceans because water responds more slowly (it can absorb heat and mix it) than air. Because the Arctic is bordered by large Northern Hemisphere land masses, it is greatly influenced by rapidly rising temperatures on these continents. This has resulted in both increasingly rapid sea ice and land ice loss in the Arctic. In contrast, Antarctica is relatively isolated from the large lower latitude land masses where much of the warming is occurring and is thus more influenced by ocean currents.

Antarctica also has meteorological features that block incoming pressure systems that would lead to more rapid change. Finally, Antarctica is a desert environment. It is so cold that the atmosphere holds little water vapor and snow fall is limited. As the atmosphere warms and carries more water vapor, snow amounts may increase, adding to the ice pack in some areas. These differences between Arctic and Antarctica responses to climate change are well captured by climate models, and observed patterns (so far) match overall predictions for these very different regions. In fact, very recent evidence of both sea ice and land ice loss in Antarctica has some scientists very nervous that the climate models may have underpredicted the vulnerability of Antarctica to climate change.

Factoids: In March 2017, both the Arctic and Antarctica had the lowest levels of sea ice in March since records were started in 1979.

Some Antarctica glaciers have shown a rapid increase in flow into the oceans, losing up to 25 feet per year in thickness.


The science all depends on computer models that fail to take many factors such as cloud formation into account. There are many feedback loops that we don’t understand. How can we be sure these models are reliable? Isn’t there some chance that climate change is being overhyped?

Evidence: That some atmospheric gases including carbon dioxide trap heat that would otherwise be irradiated back into space was first understood by scientists in the 1860s. There is a tremendous amount of information that has been collected on carbon dioxide levels in the atmosphere at times when the Earth was much warmer and much colder. It is clear that warm temperatures and high levels of CO2 go together. It is also well understood that a warmer atmosphere can hold more water vapor and that patterns of precipitation and the intensity of storms will be affected. None of that depends on modeling.

The modeling is done to project the most likely temperature increases when carbon dioxide reaches specific concentrations. And because the warming is slow relative to the rapid buildup of CO2 (it takes a long time to heat up the oceans), precisely when those temperature impacts will be experienced involves some uncertainties.

Factoid: Without the presence of greenhouse gases, the average temperature on Earth would be 0° F rather than the 59° F temperature average we experience today.


Wouldn’t it be cheaper to adapt to climate change or offset the impacts of CO2 with geoengineering rather than abandon the benefits of abundant and cheap energy to meet our needs?

Evidence: There is no doubt that we need to continue to adapt to climate change. Some adaptation is already occurring, including, for example, efforts to shift infrastructure to be less vulnerable to flooding or build up coastal defenses. But even if we stopped greenhouse gas emissions today, more warming and associated impacts will occur because the long-lived gases that have accumulated in the atmosphere have not had their full effect yet.

Many studies have examined whether it is cheaper to reduce emissions or cheaper to adapt to the higher temperatures that will come if we don’t. They generally conclude that taking action now is cheaper. One 2015 study found that the mitigation to meet the goals of the Paris Agreement would cost $11 trillion by 2100. But we would also have to spend $8 trillion adapting to the climate change that will occur anyway. Without the mitigation effort, those adaptation costs would be $20 trillion. Since then, the costs of renewable energy have been dropping, with wind and solar energy prices now decidedly cheaper than coal and in some places, rivaling natural gas. In other words, clean energy is increasingly cost-competitive with traditional fossil fuel energy.

The richest nations can more readily afford adaptation; but they are also the source of emissions which will devastate the poorest countries that cannot.

Factoid: An October 2015 study published in Nature Climate Change suggests that a combination of high temperature and high humidity may make it impossible for humans to survive in much of the Persian Gulf region by 2100. Outdoor activities, from supporting oil extraction to attending the Hajj, would become literally impossible.


The U.S. has reduced its emissions dramatically since 2007. Why should we do more that might harm the competitiveness of our economy if other nations such as China and India have not taken real action?

Evidence: It is true that China now emits more greenhouse gases each year than the U.S. But that is a recent development. For the 150 years before 2007, the U.S. and Europe were the top emitters. But if you measure emissions on a per capita basis, Americans actually generate twice as much carbon emissions as the Chinese. Carbon dioxide stays in the atmosphere a very long time—some of it for hundreds of years. The current increases in temperatures are the result of the carbon dioxide that has accumulated in the atmosphere over a very long time, and during most of that time, Europe and the U.S. were the top emitters.

More importantly, however, nations like China and India are taking much stronger and decisive action to curb their emissions. China, in particular, has already committed to institute a cap-and-trade program to reduce emissions from industrial sources, to putting 7 million new electric vehicles on its roads every year by 2025, and is now discussing when to discontinue internal combustion engines altogether. In contrast, the U.S. in the past 12 months has announced its intention to leave the Paris Agreement, rolled back the Clean Power Plan and stated its intention to promulgate more lenient rules governing tailpipe emissions.

The risk in these actions by the U.S. is that the rest of the world would accelerate their commitments of research, technology and development in this area, and leave the U.S. behind.

Factoid: Since 2007, U.S. greenhouse gas emissions have decreased by 12.2 percent; emissions from China have increased by 50 percent but are expected to peak between 2025 and 2030.


Most of the increase in global CO2 emissions over the next few decades will occur in developing countries as their populations move to middle class lifestyles. Aren’t other human goals such as clean drinking water, an adequate diet, education, and good health care enabled by access to energy and higher levels of energy consumption equally important?

Evidence: Access to clean energy remains one of the principal needs in the poorest countries as it enables the delivery of other services. However, energy development in these nations need not follow the same fossil fuel-intensive pathway taken by the U.S. (and, more recently, China) to achieve economic growth.

In September 2015, the United Nations adopted a suite of Sustainable Development Goals that, if achieved, would protect the planet and secure education and clean water for all. Doing so without adding to climate change is a fundamental principle woven into many of the development goals. Failure to address climate change can make achievement of these other goals more challenging, since climate change may increase chronic drought and change water flows and temperatures in ways that can affect water quality, fisheries, and other conditions relevant to human well-being.

Factoid: Nearly one in five people lack access to electricity; 3 billion people use wood, coal, charcoal, or animal waste for cooking and heating. Burning these fuels has adverse impacts on human health and contributes to air pollution being the leading environmental cause of death globally.


There isn’t much I can do personally about global warming. So why should I waste time trying to understand it?

Evidence: Global warming is an international problem that will take actions and policies by all nations working together. But it is also a matter for personal action. The greatest contribution to global warming comes from carbon dioxide emissions that occur as we use energy. We can all reduce emissions by changing the types and amounts of energy we use. We can buy vehicles and appliances that are more efficient. We can test-drive an electric vehicle the next time we trade in our car. We can learn to operate the smart thermostats that are in our homes and offices to reduce cooling and heating demand. One of the greatest recent changes in electricity demand has resulted from replacing incandescent bulbs with CFLs and LEDs, a choice that depends on individual consumer action.

But do keep your eye on what your city, state and national governments are doing. They will only do more to address the threat of global warming if we fully appreciate and express the need for action.

Factoid: The Department of Energy estimates that by 2027, LED lighting will reduce electricity demand by 348 TWh—an amount equivalent to roughly 28% of all the electricity generated in the U.S. from utility scale coal fired units in 2016, and representing a total savings of roughly $30 billion.