As of this October, the Earth had warmed by about 0.8 degrees Celsius since 1880, when tracking began at a global scale. 1. How much is the planet heating up?0.8C is actually a significant amount.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, but as an average over the surface of an entire planet it is actually high, which explains why much of the land ice on the planet 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 400000 Hiroshima atomic bombs exploding across the planet every day.2. How much trouble are we in?For future generations, big trouble.Over the coming 25 or 30 years, scientists say, the climate is likely to resemble that of today, just warmer. Rainfall will be heavier , 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 probably be more intense . In the longer term, s cientists fear climate effects so severe that they might produce waves of refugees, precipitate the sixth mass extinction of plants and animals in 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 centuries, but experts cannot rule out abrupt changes, such as a collapse of agriculture, that would throw society into chaos .3. Is there anything I can do?Fly less, drive less, waste less.There are lots of simple ways to reduce your own carbon footprint, and most of them will save you money. You can use solar power, use less electricity, waste less food and eat less meat. Perhaps the biggest single thing individuals can do on their own is to take fewer plane trips.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.4. What's the optimistic scenario?Several things have to break our way.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 adapt to the changes; human society develops much greater political will to bring emissions under control; and major technological breakthroughs limit emissions. Scientists say the odds of all these things breaking our way are not very high, and banking on a rosy scenario without any real plan would be dangerous. They believe the only way to limit the risks is to limit emissions.5. What's the worst-case scenario?There are many.Perhaps the single greatest fear is a collapse of food production, accompanied by spiralling prices and mass starvation. 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 the loss of trillions of dollars worth of property and other assets. Scientists also worry about other wild-card scenarios like the predictable cycles of Asian monsoons becoming less reliable. Billions of people depend on the monsoons to supply them with water for crops. So any disruptions would be catastrophic .6. Will a tech breakthrough help us?Even Bill Gates says don't count on it, unless we commit the cash.Even 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. People like Bill Gates have argued that crossing our fingers and hoping for technological miracles is not a strategy - and we have to spend the money that would make these things more likely to happen.7. How much will the seas rise?The real question is not how high, but how fast.The ocean is rising at a rate of about 30cm 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. 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 49m over an unknown period.8. Are the predictions reliable?They're not perfect, but they're grounded in solid science.Climate science does contain uncertainties . 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 feedback will intensify the warming; some of them could even partially 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.9. Why do people question climate change?Hint: ideology.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. 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.10. Will anyone benefit from global warming?In certain ways, yes.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.11. Is there any reason for hope?If you share this with 50 friends, maybe.A deal that is likely to be reached in Paris in December will commit nearly every country to some kind of action. Religious leaders like Pope Francis are speaking out. Low-emission technologies, such as electric cars, are improving. 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.New York Times..