Climate Science

Q. What's the Greenhouse Effect?

A. The Greenhouse Effect is responsible for making our planet habitable. This phenomenon, well known since the early 1800’s, is responsible for raising the average temperature of the earth’s surface by about 59° F. It occurs when gases in the atmosphere absorb heat energy from the earth’s surface and release it back into the atmosphere, warming the planet just a little bit each time. You can learn more about the Greenhouse Effect here:, and here:


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Q. What are greenhouse gases?

A. Certain gases have properties that allow them to absorb and emit energy in the infrared (heat) part of the energy spectrum. When these gases occur in the atmosphere, they are called greenhouse gases (GHG). They tend to absorb energy from one direction -- the surface -- and release it in all directions. Some of this energy stays in the atmosphere instead of radiating out into space. This warms things up, like a greenhouse. The most common greenhouse gases are water vapor, carbon dioxide and methane, in that order.


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Q. Isn't water vapor the most important greenhouse gas?

A. Water vapor is the most abundant greenhouse gas, making up anywhere from 0.1% to 3 or 4% (40,000 ppm) of the atmosphere, and contributing about 60% of greenhouse warming. But water vapor is in constant balance with the environment, precipitating into clouds and rain, or evaporating from the ocean surface. That makes water more an amplifier than a driver of global warming. Humans directly influence the water cycle by changing air temperatures with increased CO2 concentrations. Warmer air holds more moisture (about 7% per degree C), so increasing carbon dioxide allows an increase in atmospheric water vapor, which increases the greenhouse effect. Warmer oceans also intensify the water cycle.


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Q. Why is carbon dioxide such a big deal?

A. Although carbon dioxide (CO2)makes up only a small fraction of the atmosphere, about 400 ppm or 0.04%, it still contributes about 25% of greenhouse warming. Once CO2 gets in the atmosphere, it sticks around for a long time: about 100 years or more. Unlike water vapor, humans do have a direct impact on CO2 concentrations. Every gallon of gasoline we burn turns into about 20 pounds of CO2 which adds just a little more heat to the greenhouse for decades to come. Humans have burned enough fossil fuels during the industrial era to increase historical CO2 averages by about 45%. Since 1954, measured atmospheric CO2 has increased from 315 ppm to 400 ppm. Estimates of the preindustrial levels before direct measurements are in the range 280 to 300 ppm.


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Q. What about methane?

A. Methane, CH4 or natural gas, is in the news a lot these days. That’s mostly because recent hydrofracturing (fracking) technology has made vast fields of it cheap to produce. This is a good news / bad news story.


Here’s the good news: Methane produces half the CO2 of coal for the same amount of energy. For that reason it is sometimes called a bridge fuel to a low carbon future. Methane doesn’t stick around as long as CO2. It combines with oxygen compounds in the air to form CO2. And methane is less than 2 ppm concentration in the atmosphere.


But then there’s the bad news. Methane is as much as 80 times more potent than CO2 in the first decade after it is released. And methane production leaks. Often as much as 7 – 10%. That wipes out any CO2 advantage over coal. As a bridge to the future, money spent on methane may be money not spent on renewables, giving us a costly bridge to nowhere. Finally, methane concentration has roughly tripled in the last century and continues to rise, mostly due to human activity.


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Q. Isn't the climate always changing?

A. The climate is a dynamic system with natural variations as well as predictable responses to inputs, or “forcings” with warming or cooling over time. The ice ages are thought to be caused by changes in the earth's orbit. Climate changes can be abrupt, for rare forcings like meteor collisions, but usually they occur over tens or even hundreds of thousands of years. For the last 10,000 years, encompassing the development of human civilization, the climate has been pretty warm and stable. This is known as the Holocene Epoch. Many scientists claim that we are leaving the Holocene and entering a new epoch marked by human influence on planetary ecosystems. They call it the Anthropocene.


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Q. What's Global Warming?

A. Global Warming, or Anthropogenic Global Warming (AGW) is usually a term applied to the current cycle of climate change. It differs from those in the past in that it’s happening extremely quickly – decades, not millennia – and is caused primarily by human activities, including deforestation, agriculture and meat production. The primary human forcing is the increase in greenhouse gases, mainly CO2 from the massive burning of fossil fuels over the last 150 years. The lower levels of the atmosphere, including the surface air temperature, warm while the upper air levels of the stratosphere cool when CO2 levels rise. Observations from weather stations worldwide confirm these changes.


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Q. How do we know we're responsible?

A. The idea that CO2 produced by burning fossil fuels could warm the planet is not a new one. A Swedish Nobel Laureate, Svante Arrhenius, first calculated in 1896 that a doubling of CO2 in the atmosphere as a result of industrialization would increase global temperatures by about 5°C.


Reasonably good estimates can be made of how much coal and oil and gas have been converted to CO2 since Arrhenius’ time. There’s rough agreement with the amount of increase we’ve measured since then, particularly when absorption of CO2 by the oceans is also considered. We can trace the source of the excess carbon in the atmosphere to fossil fuels by “carbon dating”. The same 14C isotope that allows us to tell the age archaeological materials has disappeared from fossil carbon that’s been underground for millions of years. The measured reduction of 14C in the atmosphere matches what would be expected from burning fossil fuels.


The Intergovernmental Panel on Climate Change (IPCC), a conservative body of climate scientists, has produced five Assessment Reports over the last 25 years. These reports evaluate and summarize the state of research on climate change. They usually underestimate the rapidity of the changes. Their most recent report in 2013 concludes “It is extremely likely that human influence has been the dominant cause of observed warming since 1950”. The confidence level that global warming is real and caused by humans is now at 95% -- essentially the same as for the link between tobacco and cancer.


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Q. How warm will it get?

A. If we keep burning fossil fuels at the current rates, we can expect to see increases of 3 to 5°C by the end of this century. We have already locked in about 1°C of warming. It is still possible, with heroic effort, to stay below 2°C of warming, but that is becoming increasingly unlikely. Even if we stop producing excess greenhouse gas immediately the extra greenhouse effect will stay locked in for centuries.


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Q. Didn't global warming stop 15 years ago?

A. No. The last decade was the warmest on record, beating out the decade before that, which beat out the decade before it. The temperature record is a very noisy one. Depending on how you pick your end points, short sections of the graph can produce negative averages, even when the whole graph shows an unrelenting upward slope.


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Q. Where does all that heat go?

A. There are many ways to measure where the heat goes in the planetary system. Land surface temperature average is only one. The oceans absorb the vast majority of added heat, so a minor shift in ocean heat absorption can have a major impact on air temperatures. It also takes a lot of heat to melt ice, even if the temperature doesn't increase. About 2% of the total heat from global warming is absorbed by melting glaciers and ice sheets.


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Q. What are the major impacts of Global Warming?

A. In addition to increasing average temperatures, global warming adds energy to the climate system. As things get more energetic, expect to see more extreme warm weather events and in some areas an increase in the frequency and intensity of rainfall. The most recent report from the IPCC deals specifically with climate change impacts. Among others, the report identifies: “starvation, poverty, flooding, heat waves, droughts, war and disease [are] likely to worsen as the world warms from man-made climate change.”


As the arctic ice melts, the darker oceans absorb more energy than the white and reflective ice, causing the polar region to warm even faster. This weakens the jet stream, causing weather patterns to get stuck for longer periods and make weird excursions from their historic patterns.


Beyond that, global warming will trigger sea level rise, both because warmer water expands and because land-based ice is melting. And as the oceans absorb CO2 they are becoming more acidic, create stress on reef systems and fish populations.


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Q. Why should I care?

A. Not only will global warming cause massive economic disruption due to extreme weather disasters, it will also disrupt crop growing patterns and water supplies, causing great hardship in many of the poor countries around the world. This is a direct violation of the Biblical mandate to care for “the least of these”. As stewards of the earth we must accept responsibility for polluting the air with unacceptable levels of CO2 and abandoning our children's future prosperity and peace.


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Q. How much carbon can we burn?

A. The IPCC released a summary in Sept. 2013 of the first part of their fifth Assessment Report. For the first time, it contained a “carbon budget” that limits total burnable carbon to one trillion metric tons, or 1000 GTons to keep warming below 2° C. Humanity has already burned a little more than half that much. We are presently burning about 25 GTons per year and still increasing our rate of consumption.


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Q. How much carbon is there?

A. Fossil fuel companies have identified about 3000 GTons of carbon reserves as part of the capital assets on their books. That’s 6 times more than the science says we can afford to burn. And still, fossil fuel companies spend hundreds of millions of dollars a day looking for more.


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Q. We've got time, don't we?

A. It took us about 150 years to burn the first half of our carbon budget. Given the current projections, if nothing changes, we will completely bankrupt our remaining budget by around 2040. That only gives us about 25 years after which we need to completely stop releasing CO2 into the atmosphere. Of course, the sooner we start scaling back our fossil fuel consumption, the longer we’ll have until we reach that limit. But we have never yet been able to reduce our global CO2 production, let alone eliminate it at the rate demanded by the science.


Many scientists are concerned that these limits don’t go far enough. Even at current warming levels we run the risk of reaching new climate states that civilization has never experienced. When the arctic melts, reflective ice is replaced with dark ocean, causing even more heat to be absorbed. This is called the albedo effect. And there are huge stockpiles of methane frozen in the arctic tundra and sea beds that could be released to cause more global warming as temperatures in the arctic rise faster than in other parts of the globe.


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Q. Fossil fuel companies will do the right thing, won't they?

A. Companies are good at making money; people are good (or not) at doing the right thing. Fossil fuel companies are very good at making money. They are the most profitable corporations the world has ever seen. They will do what they need to do to keep making money. Right now that means turning all their carbon assets into CO2. In the future, with the right laws or regulations or tax structure, they may find other ways to make their money. That will be up to us.


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Q. Where can I learn more?

A. Visit the Resources page on this website for articles and other information.


An overview of “Climate Change Evidence & Causes” from the Royal Society and the US National Academy of Sciences:


To learn more about climate change, go here:


For current news on climate change, visit .


For answers to the 100 most repeated climate myths, see:


For the latest from the Intergovernmental Panel on Climate Change:


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