Even people who accept that climate destabilization is a big problem have questions about it. My sense of urgency about it grew as various building blocks of understanding fell into place. In everyday encounters with the news, people are unlikely to hear answers to any of these questions. These are some of the questions I've encountered, and answers that follow from what I've read.
CO2 IS A PART OF LIFE. HOW CAN IT POSSIBLY BE DANGEROUS?
Balance is everything. There are many examples of how something that is beneficial in moderate amounts becomes dangerous in excess. Water is essential to life, but that doesn't mean we want it flooding the basement. Fire can cook food and heat the house, but too much of it burns the house down. Rain can sustain a garden. Too much rain will wash it away. Medicine can save a life or take a life, according to how much is consumed.
Carbon dioxide (CO2) is no different. The amount of it in the atmosphere determines whether its presence is beneficial or endangers life on earth. Venus, to take an extreme example, is 850 degrees on its surface not so much because it is closer to the sun but because its atmosphere is packed with CO2. By taking long-dormant hydrocarbons from underground and burning them to form CO2 gas, we are shifting the balance in the atmosphere.
HOW MUCH HAS ATMOSPHERIC CO2 INCREASED SINCE INDUSTRIALIZATION?
40%, most of it attributable to human activity.
BUT HOW DO WE KNOW THE STEADY INCREASE IN CO2 IN THE ATMOSPHERE IS LARGELY DUE TO BURNING FOSSIL FUELS?
The carbon in CO2 comes in various forms, or isotopes, that can be measured. The carbon that has been buried underground as fossil fuel for many millions of years has isotopes in different proportions to the carbon that's been above ground all that time. As more and more of the underground carbon in fossil fuels is burned, thereby releasing additional CO2 into the air, the change in the proportion of carbon isotopes in the atmosphere can be measured.
WON'T THE EXTRA CO2 GO AWAY AFTER AWHILE?
Everyone's seen smoke dissipate and fade away. Nature can break down many kinds of pollutants. But once hydrocarbons have been dug up and burned, the CO2 pollution will impact the earth's climate for hundreds or thousands of years.
HOW DOES CO2 IN THE ATMOSPHERE HEAT THE EARTH?
Glass in a window, like CO2, is invisible and unassuming, and yet they both have great power. A car becomes burning hot inside if left in the sun on a summer day with the windows closed. This happens in part because glass has an attribute that can be wonderful or vexing, depending on the situation. It allows the sun's light energy in, but blocks the resulting heat energy from escaping. Light energy enters the car through the window, gets absorbed by the upholstery, which then releases the solar energy as heat. The heat energy being released by the upholstery has a longer wavelength that cannot escape through the windows. As more solar energy enters, with no way to escape by either radiation or convection, the car gets hotter and hotter. This is known as the greenhouse effect.
CO2 in the atmosphere behaves much like glass in a car. The sun's light energy comes through the atmospheric CO2 unimpeded, the earth absorbs that light energy, then releases it as heat, a portion of which is prevented from escaping back into space by the atmospheric CO2. The more CO2 in the atmosphere, the more heat trapped on earth. Some CO2 is beneficial; too much threatens the climatic balance.
If sunlight hits snow or, for instance, a light-colored roof, then it is not turned into heat but instead reflects back out into space as light energy, unimpeded by CO2 in the atmosphere. That's why the polar ice cap, and light-colored roofs, help reduce global warming.
For more on the greenhouse effect, here's a link:
WHY IS THE CO2 THAT COMES OUT OF TAILPIPES AND CHIMNEYS A PROBLEM WHEN PEOPLE NATURALLY EXHALE CO2?
The CO2 we and other living things exhale contains carbon that comes from the above-ground cycling of carbon. Plants absorb CO2 from the air and turn it into food energy. We eat the food (directly, or indirectly through animals) use the energy and exhale CO2, which in turn will be absorbed by the plants again. There's no net increase in above-ground carbon in this unending carbon cycle.
The CO2 emitted by cars, furnaces, and other machines, however, contains carbon that was previously buried underground in fossil fuels. The machines that consume coal or oil or natural gas essentially pump underground carbon up into the atmosphere, boosting CO2 levels and thereby heating the earth. Though some of the CO2 emitted by machines will be absorbed by plants, the net amount of carbon above ground, actively being absorbed from and released into the atmosphere, has been increased.
DOES BURNING WOOD CONTRIBUTE TO CLIMATE CHANGE
The energy in wood is, like food energy, built with CO2 that plants--in this case trees--pulled out of the air over the tree's lifespan. Burning that wood merely returns the absorbed carbon (in the form of CO2) back into the air. It makes no difference whether the wood is burned or left to decompose on the ground. Though fire will release the CO2 quickly, decomposing microorganisms eventually release the same amount of CO2 from the same amount of wood over time. Heating with a woodstove is thus a form of solar energy, just as the heat our bodies produce comes from the solar energy in food.
Since fossil fuels are made from ancient life that was buried 100s of millions of years ago, some will say that they are simply another form of solar energy. But the burial of those hydrocarbons over millions of years played an important role in creating the temperate climate in which we evolved and have thrived.
WHY WORRY ABOUT CLIMATE CHANGE, SINCE TEMPERATURES ON EARTH HAVE CHANGED BEFORE?
Historic changes in temperature were very slow, occurring over thousands or hundreds of thousands of years. Human-caused temperature changes are happening over the course of a few decades. As an analogy, the force of collision by a car crawling along at one mile per hour is much less destructive than if the car is going 100 mph. The speed of change has much to do with determining whether nature will have time to adapt.
In addition, the steady warming of the planet may trigger even more rapid changes. The ice sheets perched on Greenland, which are starting to sprout rivers deep in their interior that could lubricate their plunge into the Atlantic, hold enough ice to raise sea levels by 20 feet. Parts of Antarctica, which holds enough ice to raise sea levels 200 feet, could also become unstable. It’s hard to say when ocean acidification, thawing deposits of methane up north, and climate-driven shifts in ocean currents could trigger rapid transformations.
In addition to flooding of low-lying areas, the destabilizing of the climate will increasingly undermine the dependability of agriculture. Large numbers of refugees will put a strain on governments and international relations. A stable climate, then, is important to maintaining political and social stability.
BUT CHANGING THE TEMPERATURE OF THE EARTH'S ATMOSPHERE A COUPLE DEGREES, OR EVEN FIVE, DOESN'T SOUND LIKE MUCH.
It's easy for people to adjust to a few degrees change in outside temperature, but when we develop a fever of even a degree or two, we notice. If our body temperature rises five degrees, we're incapacitated. The physical and biological systems on land and in the ocean are as complex and sensitive to temperature change as the finely tuned physiological systems in our bodies.
SOME OF THE CLIMATE SCIENTIST'S PREDICTIONS ARE PRETTY VAGUE. WHY NOT WAIT UNTIL WE UNDERSTAND CLIMATE CHANGE MORE COMPLETELY?
Climate scientists, like doctors, are trying to understand extraordinarily complex systems. We don't expect our doctor to tell us exactly when the consequences of unhealthy behavior will become manifest, and climate scientists should not be expected to have all the answers before their warnings are taken seriously.
POLICY TO RESPOND TO TERRORIST THREATS IS OFTEN BASED ON WORST CASE SCENARIOS. WHY DO WE TEND TO PLAY DOWN WORST CASE SCENARIOS FOR CLIMATE CHANGE?