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Despite the unmistakable evidence that climate change is happening and that the effects we're already experiencing are mostly caused by our own actions, it's not uncommon to meet deniers—even around your own family's holiday table.
Some of the misinformation that creeps into the doubters' discussions are the lingering leftovers of years of deliberate peddling of misinformation, often by fossil fuel interests.
Some of it persists because, face it, not everybody is well versed in the scientific consensus, which is based on multiple streams of evidence from dozens of specialized disciplines. Who can keep up?
Even those who are thankful this year for the work of the United States Global Change Research Program, which just published an update of the latest science, may not have studied all the details.
With that in mind, we asked you to share some of the common myths and errors you hear at family gatherings. And we've pieced together some short answers from that state-of-the-science report and other authoritative sources.
'Brrrr, it's cold out. Is there really global warming?'
Just ask your parents and grandparents. They'll probably remember that winters were colder when they were your age. And on average, they'd be right. If you start with their reminiscences, it's easy to turn the conversation toward today's realities.
Sure, it still gets cold in the winter—sometimes too cold for comfort! But "the frequency of cold waves has decreased since the early 1900s," the updated science report says.
"The temperatures of extremely cold days and extremely warm days are both expected to increase," the report predicts—with very high confidence. "Cold waves are projected to become less intense while heat waves will become more intense. The number of days below freezing is projected to decline while the number above 90°F will rise."
The holidays of November and December will still bring sweater weather to many Americans. But it's already clear that they won't be like the olden days.
'What about the Sun? Isn't climate change caused by solar activity that changes its brightness?'
The national climate report found "no convincing evidence" of this. Solar fluctuations "have been too small to explain the observed changes in climate" in the past 60 years.
The Sun, of course, is the primary source of all the world's energy—even our fossil fuels were once plants and the animals that ate them. So if the strength of solar radiation fluctuates, it can affect the climate.
But scientists know that these fluctuations have been relatively small. Measurements have gotten a lot better in the satellite era, and the changes in solar activity simply don't track with the observed warming in the way that the other main influence on climate does—that is, the growing blanket of carbon dioxide that traps the heat of the Sun.
Human pollution, in short, "far exceeded" the influence of natural factors, including sunshine.
'How can you be so sure about warming when the climate computer models are uncertain?'
Even the most rudimentary climate models, starting about 50 years ago, were remarkably accurate in forecasting what has happened to the climate since then.
And they are getting better, leading scientists to become ever more confident about their conclusions.
The very first scientific consensus report by the Intergovernmental Panel on Climate Change, released in 1990, said that "unequivocal detection" of predicted warming was likely to take a decade or more to see. The second said, "the balance of evidence suggests a discernible human influence on climate." The third said most observed warming "is likely to have been due to the increase of greenhouse gases." The fourth said human causes were "very likely." The fifth and most recent, in 2014, called it "extremely likely" that more than half the warming of the past six decades was caused by our own actions.
The biggest unknown is not the uncertainties in the models—all the models point in the same direction, and the differences are matters of degree. What we don't know is whether humanity will commit to steep reductions in carbon emissions. Emissions must fall to net zero if global warming is to be stopped. On that, the science is irrefutable.
'Carbon dioxide is plant food, right? So the more of it the better.'
Research has shown that increased carbon dioxide has had a fertilizing effect on plants, boosting growth of certain vegetation in some areas over the past three decades.
But after CO2 delivers an initial jolt to some plant life, levels of plant productivity drop as most plants get saturated with CO2. Besides, plants need more than CO2 to grow—like people, they need other nutrients, too. Without an increase in those, growth plateaus.
The real problem is that with more CO2 entering the atmosphere, temperatures will rise, droughts will expand and rain patterns will change. The National Climate Assessment has said these changes will be "increasingly negative on most crops and livestock."
So, as you lapse into a post-feast food coma, tell Cousin Ralph this: Some crops might experience a growth spurt in the short term, but overall, CO2 is a threat to the quality and quantity of our food supply.
'The Arctic may be losing ice, but Antarctic ice is expanding, right? How could that be if the planet is warming?'
First, it's important to remember that the North Pole and the South Pole are two very different places—polar opposites, right? The Arctic is mostly an ocean (and it has polar bears), and Antarctica is a big continent (with penguins). We don't expect to see the same things.
True, Antarctica's sea ice was building up for a while, but recent observations show that's changed drastically.
The real worry is what's happening with Antarctica's ice sheets, which are anchored on the ground and on the seafloor. If warming ocean water causes the ice shelves at the edges of Antarctica's glaciers to disappear, the glaciers behind them start to flow faster, and the ice sheets could start to collapse. That's already starting to happen. The amount of ice that could ultimately be released into the ocean would cause catastrophic flooding across the planet.
The question is when the flooding will happen, and how much. According to the latest science, we may already have locked in nearly 4 feet of sea level rise from the West Antarctic Ice Sheet alone. It would probably take many centuries, but not necessarily. If we don't cut back our carbon pollution, most of it could occur in this century. And over the long term, there's even some risk of 70 feet of sea level rise over a span of 10,000 years! Future generations may well thank us if we can avoid that.