The New York Times
Short Answers to Hard Questions About Climate Change
By JUSTIN GILLIS
July 6, 2017
The issue can be overwhelming. The science is complicated. Predictions about the fate of the planet carry endless caveats and asterisks.
- What are ‘carbon emissions?’
By far the biggest factor causing global warming is the burning of fossil fuels for electricity and transportation. That process takes carbon that has been underground for millions of years and moves it into the atmosphere, as carbon dioxide, where it will influence the climate for many centuries into the future. Methane is even more potent at trapping heat than carbon dioxide, but it breaks down more quickly in the air. Methane comes from swamps, from the decay of food in landfills, from cattle and dairy farming, and from leaks in natural gas wells and pipelines.
While fossil-fuel emissions are the major issue, another major creator of emissions is the destruction of forests, particularly in the tropics. Billions of tons of carbon are stored in trees, and when forests are cleared, much of the vegetation is burned, sending that carbon into the air as carbon dioxide.
When you hear about carbon taxes, carbon trading and so on, these are just shorthand descriptions of methods designed to limit greenhouse emissions or to make them more expensive so that people will be encouraged to conserve fuel.
- How much is the planet warming up?
As of early 2017, the Earth had warmed by roughly 2 degrees Fahrenheit, or more than 1 degree Celsius, since 1880, when records began at a global scale. That figure includes the surface of the ocean. The warming is greater over land, and greater still in the Arctic and parts of Antarctica.
The number may sound low. We experience much larger temperature swings in our day-to-day lives from weather systems and from the changing of seasons. But when you average across the entire planet and over months or years, the temperature differences get far smaller – the variation at the surface of the Earth from one year to the next is measured in fractions of a degree. So a rise of 2 degrees Fahrenheit since the 19th century is actually high.
The substantial warming that has already occurred explains why much of the world’s land ice is starting to melt and the oceans are rising at an accelerating pace. The heat accumulating in the Earth because of human emissions is roughly equal to the heat that would be released by 400,000 Hiroshima atomic bombs exploding across the planet every day.
Scientists believe most and probably all of the warming since 1950 was caused by the human release of greenhouse gases. If emissions continue unchecked, they say the global warming could ultimately exceed 8 degrees Fahrenheit, which would transform the planet and undermine its capacity to support a large human population.
- How much trouble are we in?
The risks are much greater over the long run than over the next few decades, but the emissions that create those risks are happening now. This means the current generation of people is dooming future generations to a more difficult future.
Over the coming 25 or 30 years, scientists say, the climate is likely to resemble that of today, although gradually getting warmer, with more of the extreme heat waves that can kill vulnerable people. Rainfall will be heavier in many parts of the world, but the periods between rains will most likely grow hotter and drier. The number of hurricanes and typhoons may actually fall, but the ones that do occur will draw energy from a hotter ocean surface, and therefore may be more intense. Coastal flooding will grow more frequent and damaging, as is already happening.
Longer term, if emissions continue to rise unchecked, the risks are profound. Scientists fear climate effects so severe that they might destabilize governments, produce waves of refugees, precipitate the sixth mass extinction of plants and animals in the Earth’s history, and melt the polar ice caps, causing the seas to rise high enough to flood most of the world’s coastal cities.
All of this could take hundreds or even thousands of years to play out, but experts cannot rule out abrupt changes, such as a collapse of agriculture, that would throw civilization into chaos much sooner. Bolder efforts to limit emissions would reduce these risks, or at least slow the effects, but it is already too late to eliminate the risks entirely.
- Is there anything I can do about climate change?
You can reduce your own carbon footprint in lots of simple ways, and most of them will save you money. You can plug leaks in your home insulation to save power, install a smart thermostat, switch to more efficient light bulbs, turn off the lights in any room where you are not using them, drive fewer miles by consolidating trips or taking public transit, waste less food and eat less meat.
Perhaps the biggest single thing individuals can do on their own is to take fewer airplane trips; just one or two fewer plane rides per year can save as much in emissions as all the other actions combined. If you want to be at the cutting edge, you can look at buying an electric or hybrid car, putting solar panels on your roof, or both.
If you want to offset your emissions, you can buy certificates, with the money going to projects that protect forests, capture greenhouse gases and so forth. Some airlines sell these to offset emissions from their flights. You can also buy offset certificates in a private marketplace, from companies such as TerraPass; some people even give these as holiday gifts. In states that allow you to choose your own electricity supplier, you can often elect to buy green electricity; you pay slightly more, and the money goes into a fund that helps finance projects like wind farms.
Leading companies are also starting to demand clean energy for their operations. You can pay attention to company policies, patronize the leaders, and let the others know you expect them to do better.
In the end, though, experts do not believe the needed transformation in the energy system can happen without strong state and national policies. So speaking up and exercising your rights as a citizen matters as much as anything else you can do.
- What’s the optimistic case?
In the best case that scientists can imagine, several things happen: Earth turns out to be less sensitive to greenhouse gases than currently believed; plants and animals manage to adapt to the changes that have already become inevitable; human society develops much greater political will to bring emissions under control; and major technological breakthroughs occur that help society to limit emissions and to adjust to climate change.
Some technological breakthroughs are already making cleaner energy more attractive. In the United States, for instance, coal has been losing out to natural gas as a power source, as new drilling technology has made gas more abundant and cheaper; for a given amount of power, gas cuts emissions in half. In addition, the cost of wind and solar power has declined so much that they are now the cheapest power source in a few places, even without subsidies.
Unfortunately, scientists and energy experts say the odds of all these things breaking our way are not very high. The Earth could just as easily turn out to be more sensitive to greenhouse gases as less. Global warming seems to be causing chaos in parts of the natural world already, and that seems likely to get worse, not better. So in the view of the experts, simply banking on rosy assumptions without any real plan would be dangerous. They believe the only way to limit the risks is to limit emissions.
- What’s the worst case?
Perhaps the greatest fear is a collapse of food production, accompanied by escalating prices and mass starvation. It is unclear how likely this would be, since farmers are able to adjust their crops and farming techniques, to a degree, to adapt to climatic changes. But we have already seen heat waves contribute to broad crop failures. A decade ago, a big run-up in grain prices precipitated food riots around the world and led to the collapse of at least one government, in Haiti.
Another possibility would be a disintegration of the polar ice sheets, leading to fast-rising seas that would force people to abandon many of the world’s great cities and would lead to the loss of trillions of dollars' worth of property and other assets. In places like Florida and Virginia, towns are already starting to have trouble with coastal flooding.
Scientists also worry about other wild-card events. Will the Asian monsoons become less reliable, for instance? Billions of people depend on the monsoons to provide water for crops, so any disruptions could be catastrophic. Another possibility is a large-scale breakdown of the circulation patterns in the ocean, which could potentially lead to sudden, radical climate shifts across entire continents.
- Are the predictions reliable?
The idea that Earth is sensitive to greenhouse gases is confirmed by many lines of scientific evidence. For instance, the basic physics suggesting that an increase of carbon dioxide traps more heat was discovered in the 19th century, and has been verified in thousands of laboratory experiments.
Climate science does contain uncertainties, of course. The biggest is the degree to which global warming sets off feedback loops, such as a melting of sea ice that will darken the surface and cause more heat to be absorbed, melting more ice, and so forth. It is not clear exactly how much the feedbacks will intensify the warming; some of them could even partly offset it. This uncertainty means that computer forecasts can give only a range of future climate possibilities, not absolute predictions.
But even if those computer forecasts did not exist, a huge amount of evidence suggests that scientists have the basic story right. The most important evidence comes from the study of past climate conditions, a field known as paleoclimate research. The amount of carbon dioxide in the air has fluctuated naturally in the past, and every time it rises, the Earth warms up, ice melts and the ocean rises. A hundred miles inland from today’s East Coast of the United States, seashells can be dug from ancient beaches that are three million years old, a blink of an eye in geologic time.
These past conditions are not a perfect guide to the future, because humans are pumping carbon dioxide into the air far faster than nature has ever done. But they show it would be foolish to assume that modern society is somehow immune to large-scale, threatening changes.
- Why do people question the science of climate change?
Most of the attacks on climate science are coming from libertarians and other political conservatives who do not like the policies that have been proposed to fight global warming. Instead of negotiating over those policies and trying to make them more subject to free-market principles, they have taken the approach of blocking them by trying to undermine the science.
This ideological position has been propped up by money from fossil-fuel interests, which have paid to create organizations, fund conferences and the like. The scientific arguments made by these groups usually involve cherry-picking data, such as focusing on short-term blips in the temperature record or in sea ice, while ignoring the long-term trends.
The most extreme version of climate denialism is to claim that scientists are engaged in a worldwide hoax to fool the public so that the government can gain greater control over people’s lives. As the arguments have become more strained, many oil and coal companies have begun to distance themselves publicly from climate denialism, but some are still helping to finance the campaigns of politicians who espouse such views.
- Will anyone benefit from global warming?
Countries with huge, frozen hinterlands, including Canada and Russia, could see some economic benefits as global warming makes agriculture, mining and the like more possible in those places. It is perhaps no accident that the Russians have always been reluctant to make ambitious climate commitments, and President Vladimir V. Putin has publicly questioned the science of climate change.
However, both of those countries could suffer enormous damage to their natural resources; escalating fires in Russia are already killing millions of acres of forests per year. Moreover, some experts believe countries that view themselves as likely winners from global warming will come to see the matter differently once they are swamped by millions of refugees from less fortunate lands.
- Will a technology breakthrough help us?
As more companies, governments and researchers devote themselves to the problem, the chances of big technological advances are improving. But even many experts who are optimistic about technological solutions warn that current efforts are not enough. For instance, spending on basic energy research is only a quarter to a third of the level that several in-depth reports have recommended. And public spending on agricultural research has stagnated even though climate change poses growing risks to the food supply. People like Bill Gates have argued that crossing our fingers and hoping for technological miracles is not a strategy — we have to spend the money that would make these things more likely to happen.
- Is crazy weather tied to climate change?
Scientists have published strong evidence that the warming climate is making heat waves more frequent and intense. It is also causing heavier rainstorms, and coastal flooding is getting worse as the oceans rise because of human emissions. Global warming has intensified droughts in regions like the Middle East, and it may have strengthened a recent drought in California.
In many other cases, though, the linkage to global warming for particular trends is uncertain or disputed. That is partly from a lack of good historical weather data, but it is also scientifically unclear how certain types of events may be influenced by the changing climate.
Another factor: While the climate is changing, people’s perceptions may be changing faster. The Internet has made us all more aware of weather disasters in distant places. On social media, people have a tendency to attribute virtually any disaster to climate change, but in many cases there is little or no scientific support for doing so.
- How much will the seas rise?
The ocean is rising at a rate of about a foot per century. That causes severe effects on coastlines, forcing governments and property owners to spend tens of billions of dollars fighting erosion. But if that rate continued, it would probably be manageable, experts say.
The risk is that the rate will accelerate markedly. If emissions continue unchecked, then the temperature at the Earth’s surface could soon resemble a past epoch called the Pliocene, when a great deal of ice melted and the ocean rose by something like 80 feet compared to today. A recent study found that burning all the fossil fuels in the ground would fully melt the polar ice sheets, raising the sea level by more than 160 feet over an unknown period. Many coastal experts believe that even if emissions stopped tomorrow, 15 or 20 feet of sea-level rise is already inevitable.
The crucial issue is probably not how much the oceans are going to rise, but how fast. And on that point, scientists are pretty much flying blind. Their best information comes from studying the Earth’s history, and it suggests that the rate can on occasion hit a foot per decade, which can probably be thought of as the worst case. Even if the rise is much slower, many of the world’s great cities will flood eventually. Studies suggest that big cuts in emissions could slow the rise, buying crucial time for society to adapt to an altered coastline.
- Will the seas rise evenly across the planet?
Many people imagine the ocean to be like a bathtub, where the water level is consistent all the way around. In fact, the sea is rather lumpy — strong winds and other factors can cause water to pile up in some spots, and to be lower in others.
Also, the huge ice sheets in Greenland and Antarctica exert a gravitational pull on the sea, drawing water toward them. As they melt, sea levels in their vicinity will fall as the water gets redistributed to distant areas.
How the rising ocean affects particular parts of the world will therefore depend on which ice sheet melts fastest, how winds and currents shift, and other related factors. On top of all that, some coastal areas are sinking as the sea rises, so they get a double whammy.
- How does agriculture affect climate change?
The environmental pressures from global agriculture are enormous. Global demand for beef and for animal feed, for instance, has led farmers to cut down large swaths of the Amazon forest.
Brazil adopted tough oversight and managed to cut deforestation in the Amazon by 80 percent in a decade. But the gains there are fragile, and severe problems continue in other parts of the world, such as aggressive forest clearing in Indonesia.
Scores of companies and organizations, including major manufacturers of consumer products, signed a declaration in New York in 2014 pledging to cut deforestation in half by 2020, and to cut it out completely by 2030. The companies that signed the pact are now struggling to figure out how to deliver on that promise.
Many forest experts consider meeting the pledge to be difficult, but possible. They say consumers must keep up the pressure on companies that use ingredients like palm oil in products ranging from soap to lipstick to ice cream. People can also help the cause by altering their diets to eat less meat, and particularly less beef.
- Will reducing meat in my diet really help the climate?
Agriculture of all types produces greenhouse gases that warm the planet, but meat production is especially harmful — and beef is the most environmentally damaging form of meat. Some methods of cattle production demand a lot of land, contributing to destruction of forests; the trees are typically burned, releasing carbon dioxide into the atmosphere. Other methods require huge amounts of water and fertilizer to grow food for the cows.
The cows themselves produce emissions of methane, a potent greenhouse gas that causes short-term warming. Meat consumption is rising worldwide as the population grows, and as economic development makes people richer and better able to afford meat.
This trend is worrisome. Studies have found that if the whole world were to start eating beef at the rate Americans eat it, produced by the methods typically used in the United States, that alone might erase any chance of staying below an internationally agreed-upon limit on global warming. Pork production creates somewhat lower emissions than beef production, and chicken lower still. So reducing your meat consumption, or switching from beef and pork to chicken in your diet, are moves in the right direction. Of course, as with any kind of behavioral change meant to benefit the climate, this will only make a difference if lots of other people do it, too, reducing the overall demand for meat products.
- Is there any reason for hope?
Scientists have been warning since the 1980s that strong policies were needed to limit emissions. Those warnings were ignored, and greenhouse gases in the atmosphere were allowed to build up to potentially dangerous levels. So the hour is late.
But after 20 years of largely fruitless diplomacy, the governments of the world are finally starting to take the problem seriously. A deal reached in Paris in late 2015 commits nearly every country to some kind of action. President Trump decided in 2017 to pull the United States out of that deal, saying it would unfairly burden American businesses. But other countries are promising to go forward with it anyway, and some states and cities have defied Mr. Trump by adopting more ambitious climate goals.
Religious leaders like Pope Francis are speaking out. Low-emission technologies, such as electric cars, are improving. Leading corporations are making bold promises to switch to renewable power and stop forest destruction.
What is still largely missing in all this are the voices of ordinary citizens. Because politicians have a hard time thinking beyond the next election, they tend to tackle hard problems only when the public rises up and demands it