Man-made climate change is here.

Climate change is a reality we can no longer ignore. We see the impacts in our everyday lives, from extreme superstorms, to heat waves, to massive wildfires and droughts. But climate denial, bankrolled by Dirty Energy companies and justified by pseudoscience, persists.

Reality Drop, inspired by Skeptical Science, is a library of science-based rebuttals to climate change deniers.

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Showing 37 myths:

• #3: Carbon dioxide isn’t the main cause of warming

  Deniers say: It's not just carbon dioxide. What about volcanoes, solar variations, methane, aerosols and clouds?
  Science says: Ask the majority of climate scientists: Man-made carbon pollution is the cause of the global warming we’re seeing now.
  Scientists know our climate is changing, primarily due to carbon pollution from the burning of dirty energy like oil and coal. It's true that other factors affect our climate, including other greenhouse gases such as methane. Solar variation, volcanoes and clouds all affect the climate, too. But scientists take all these factors into account and weigh the contributions that each one makes to our climate. When they do, it's clear that man-made carbon dioxide pollution is overwhelmingly responsible for the warming we’re experiencing now.
• #4: Carbon dioxide lags temperature

  Deniers say: Global warming happens first, carbon dioxide rises afterward.
  Science says: Carbon dioxide is a control knob on our climate. The more we pollute, the warmer it gets.
  Our climate has warmed over the last 130 years because of carbon pollution from human activities. At other times in the Earth's history, long before humans started burning fossil fuels, the climate warmed for other reasons, such as changes in the Earth's orbit. As the temperature increased in the past, oceans also released more carbon dioxide because warm water holds less carbon dioxide than cold water. This led to more warming, and even more carbon dioxide as a result. The bottom line is this: The fact that global warming happened for different reasons hundreds of thousands of years ago does not change the fact that today, human activity is responsible for climate change. We are putting 35 billion tons of carbon pollution into the atmosphere every year. And scientists agree that is the reason our planet is now warming.
• #5: There was more carbon dioxide in the past

  Deniers say: What about 400 million years ago, when CO₂ was five times higher than it is right now?
  Science says: Looking back at naturally-caused global warming hundreds of millions of years ago is a nice history lesson, but it tells us little about man-made global warming today.
  Because of pollution from dirty energy like coal, there is more carbon dioxide in the atmosphere now than in nearly a million years. More than 400 million years ago, however, carbon dioxide concentrations were much higher than today, and the world was mostly a lot warmer as well. Back then, the warming was indeed due to natural causes.
  
  What does that tell us about climate change today? Not much. The world was a completely different place 400 million years ago. The continents were in different positions. Life was almost entirely restricted to the oceans. Trees didn’t exist. Humans didn't exist. In other words, not all pre-historic climate facts are relevant to the modern climate crisis.
• #6: Carbon dioxide measurements are suspect

  Deniers say: You can’t rely on the global CO₂ data. Ice cores are inaccurate, and modern instruments are often placed near volcanoes.
  Science says: From Hawaii to Antarctica, data collected from all over the world tell us one thing: Carbon pollution is going up.
  Scientists don’t just measure carbon dioxide in one way, or in one place. Gas bubbles trapped in ice cores show us what carbon dioxide concentrations were like deep in the Earth’s past. Measurements made at the Mauna Loa Observatory in Hawaii show us that carbon dioxide has been increasing in our atmosphere. And Mauna Loa isn't the only place this pattern is seen; data from observatories in Alaska, American Samoa and Antarctica all show the same upward trend. All the measurements we have from an extensive array of sources tell us this: Carbon dioxide levels are rising.
• #7: Mauna Loa is a volcano

  Deniers say: One of the most important records of the Earth’s CO₂ concentrations is 30 miles away from a carbon dioxide-spewing volcano.
  Science says: Scientists adjust for the fact that Mauna Loa is a volcano to make sure their measurements are accurate.
  Continuous measurements taken at the Mauna Loa Observatory clearly show that carbon dioxide has been increasing in the atmosphere since 1958. And Mauna Loa isn’t the only place this pattern is seen; data from observatories in Alaska, American Samoa and Antarctica all show the same upward trend. Scientists were well aware when they selected Mauna Loa that it’s a volcano. But they also knew that most of the time, the wind blows volcanic gases (including carbon dioxide) away from the observatory. When the wind infrequently shifts, there’s an obvious spike in carbon dioxide. Measurements from the “volcano days” are removed from the Mauna Loa dataset. That's how scientists make sure the data are accurate.
• #8: Volcanoes emit more carbon dioxide than us

  Deniers say: Volcanoes are able to emit more carbon dioxide in a single day than humans could emit over centuries.
  Science says: Here's something to blow your top off: Humans send up 135 times more carbon dioxide than volcanoes.
  Think volcanoes emit more carbon dioxide than humans? You’ve got it backwards. Humans release at least 135 times more carbon dioxide to the air than volcanoes. Emissions from Mount Pinatubo, the strongest volcanic eruption over the past 50 years, amounted to just 0.2 percent of human emissions in 1991. Just 0.2 percent! By releasing 35 billion tons of carbon dioxide into the atmosphere each year, humans are the main drivers of climate change.
• #9: There’s more carbon dioxide due to natural causes

  Deniers say: CO₂ in the air comes from volcanoes, the oceans and other natural sources, not humans.
  Science says: What's causing climate change? Human beings. Just ask 97% of the top climate scientists in the world.
  How can scientists be sure that humans are increasing heat-trapping carbon dioxide? First, the carbon dioxide in the atmosphere has increased about 40 percent since humans started burning dirty energy like coal and oil on a wide scale. Second, the carbon from dirty energy has a unique chemical signature that allows scientists to tell it apart from other sources of carbon. Third, the amount of oxygen in the atmosphere is decreasing. It takes oxygen to burn trees or coal, and the more burning we do, the more oxygen we suck up. The evidence is inescapable: Humans ARE changing our climate.
• #10: Breathing causes global warming

  Deniers say: If you’re serious about wanting to reduce carbon pollution, you should stop breathing.
  Science says: Take a deep breath. Don't worry, that has nothing to do with climate change.
  A human exhales about 1 kilogram of carbon dioxide a day. That sounds like a lot when you consider there are about 7 billion of us on the planet. But the carbon we breathe out doesn’t magically appear — it comes from the carbon-based things we eat. And as you may recall, plants need carbon dioxide to make their own food via photosynthesis. So, we have a closed cycle: the carbon taken in by plants becomes food for us (either directly or indirectly), and then we breathe the carbon out ... and then plants take it in again. When we burn dirty energy, we’re adding carbon to the air that had been out of the loop for millions of years and was stored underground as deposits of coal, oil, and gas. Once we take that carbon out of the ground, it will be in our atmosphere for thousands of years to come.
• #12: Carbon dioxide is just a trace gas so it can't affect our climate

  Deniers say: How could such a small amount of carbon dioxide have any meaningful effect on the climate?
  Science says: Like alcohol or ibuprofen, even very small amounts of carbon dioxide can have huge effects.
  Yes, carbon dioxide makes up just 392 parts per million, or about 0.04% of our atmosphere. Guess what: That doesn’t mean its impact isn’t serious. That would be like saying drivers aren’t drunk if they only have a trace of blood alcohol: 0.08%. Or that ibuprofen won’t help your headache because it’s only 0.0003% of your body weight. The point is, small amounts of very active substances can have large effects. Carbon dioxide is a trace gas, but it has increased by 40% since the Industrial Revolution and is warming our planet at an incredibly fast rate. And that’s the part that matters.
• #13: Humans emit a tiny percentage of the carbon in the air

  Deniers say: There's a lot of carbon in the atmosphere and only a tiny part of it is manmade.
  Science says: Not all the carbon in the air comes from humans. Problem is, humans send up an extra dose of carbon that nature can't handle.
  Carbon cycles naturally through the environment. It is taken up by plants and breathed out by animals, and it moves back and forth between the air and the oceans. Prior to the Industrial Revolution, this natural cycle was more or less balanced. The carbon that entered the atmosphere was roughly equal to the amount that was absorbed and stored. But by burning dirty energy like oil and coal, we’re injecting “new” carbon into the cycle ⎯ carbon that used to be locked underground. The ocean and plants on land are working extra hard to absorb some of this excess, but they can’t take it all. That’s why carbon pollution is accumulating ⎯ and we have more carbon dioxide in the atmosphere than any time in nearly a million years.
• #14: More carbon dioxide has little effect

  Deniers say: So what if we're emitting a little more CO₂? That doesn't mean we're responsible for climate change.
  Science says: Carbon dioxide traps heat. The more carbon we send into the sky, the hotter it gets.
  More than a century ago, scientists figured out that carbon dioxide and other greenhouse gases trap heat. Many lines of evidence now confirm our planet is warming because of carbon pollution released when humans burn fossil fuels like oil and coal. One of the most important lines of evidence is a closer look at the wavelength, or “type,” of heat being trapped in the Earth’s atmosphere. Carbon dioxide traps specific wavelengths of heat energy, and satellite and surface measurements show that in recent decades, less heat at those specific wavelengths is escaping to space. Given that carbon dioxide concentrations in the atmosphere have increased a whopping 40% since the start of the Industrial Revolution, it’s really no wonder our planet’s temperature is rising.
• #15: Carbon dioxide emissions do not correlate with carbon dioxide concentration

  Deniers say: Human emissions of CO₂ don’t vary much from year to year, but the concentration of CO₂ in the atmosphere varies a lot. It clearly doesn’t come from us.
  Science says: We're putting more carbon into the atmosphere than nature can handle. That causes global warming.
  The concentration of carbon dioxide in the atmosphere correlates closely — but not perfectly — with the amount of carbon pollution emitted by human activities. That’s because plants, soils and the ocean take some of the carbon back out of the atmosphere. This is a good thing, because otherwise the planet would be heating up even faster than it is now. Unfortunately, we’re putting more carbon pollution into the atmosphere than natural systems can absorb, and that's why the planet is warming.
• #16: The atmosphere is saturated with carbon dioxide

  Deniers say: The more carbon we release into the atmosphere, the less it matters.
  Science says: The atmosphere isn't a sponge; it can't get "saturated" with carbon dioxide. The more carbon we put into the atmosphere, the hotter it gets.
  Deniers have argued that our atmosphere is "saturated" with carbon dioxide. In other words, they’re saying that adding more carbon dioxide to the atmosphere doesn’t strengthen the existing greenhouse effect. But carbon dioxide traps specific wavelengths of heat energy. And satellite and surface measurements show that in recent decades, less heat at those specific wavelengths is escaping to space. This is evidence that carbon dioxide is strengthening the greenhouse effect.
• #17: There's no correlation between carbon dioxide and temperature

  Deniers say: We’ve been emitting more carbon dioxide since the start of the Industrial Revolution, but temperatures go up and down from year to year.
  Science says: We have warm years and cold years, but over the long run, global temperatures have gone up.
  Carbon dioxide traps heat. We've known that since the 19th century. And as carbon pollution from dirty energy has gone up, the Earth's temperature has increased as well. Since 1880, the world has warmed nearly 1.5 degrees Fahrenheit (0.8 degrees Celsius) — and more than half the warming has occurred since 1979. But natural variations mean that the increase isn't steady from year to year. One year might be unusually cold, the next might be unusually warm. That’s why the lines on a temperature graph zigzag from year to year. When scientists filter out the “noise” from short-term variation, clear trends emerge. The global average temperature over the last hundred years has risen steadily along with carbon pollution.
• #18: Carbon dioxide only causes 35% of global warming

  Deniers say: Some scientists say that CO₂ doesn’t even account for half of the warming we’ve seen recently.
  Science says: What's the biggest cause of global warming today? Man-made pollution from carbon dioxide.
  A 2010 study found that methane, ground-level ozone, and black carbon (i.e., soot) increase the global warming effect of carbon dioxide by 65 percent. Some people misread this as a suggestion that carbon dioxide was only responsible for 35 percent as much global warming as previously believed. What it actually says is that these short-term pollutants cause warming IN ADDITION to carbon dioxide. Nothing in the study changes the fact that carbon dioxide is the main cause of the warming we’re seeing today.
• #19: It's not us

  Deniers say: Okay, climate change is happening. But it has natural causes, and humans have nothing to do with it.
  Science says: Ask the majority of climate scientists: Man-made carbon pollution is the cause of global warming.
  97 percent of top climate scientists and every major National Academy of Science agree that man-made pollution is warming our climate. Here’s how they know. First, the concentration of carbon dioxide in the atmosphere has increased about 40 percent since humans started burning dirty energy like coal. Second, the carbon from dirty energy has a unique chemical signature that differentiates it from other sources of carbon — so we can confirm that it's coming from us. Third, we know it is carbon — not natural forces like the sun — that's responsible for the recent increase in global temperatures. Why? The lower level of the atmosphere is warming, while the middle layer is cooling. If the sun were responsible for most of the recent temperature change on Earth, both layers of the atmosphere would be warming. The evidence is inescapable: Humans ARE changing our climate.
• #20: Humans are too insignificant to affect global climate

  Deniers say: How could we have an impact on an old and enormous planet that's been regulated by natural processes for billions of years? It’s impossible.
  Science says: Thanks to humans, the carbon in the atmosphere has gone up by 40%. It's no surprise that would have a big impact on our climate.
  It's true that for most of history, human beings sent insignificant amounts of carbon pollution into the atmosphere — not enough to affect our climate. Since the Industrial Revolution, however, we have been burning fossil fuels like coal and oil on an unprecedented scale. We have increased the concentration of carbon dioxide in our atmosphere by about 40 percent — and this enormous increase in carbon dioxide has warmed our planet.
• #22: It’s the sun

  Deniers say: The sun's energy has increased over the last several hundred years, and that's why Earth is getting warmer.
  Science says: The sun is responsible for a lot -- like sustaining life. But humans are responsible for the global warming we see today.
  The sun is our primary source of energy here on Earth, and yes, it most definitely keeps us warm. But here’s the thing — without greenhouse gases like carbon dioxide in our atmosphere, the Earth would be a lot colder because most of the sun’s heat would quickly disappear into space. Today, we’re putting more and more heat-trapping carbon pollution in the atmosphere by burning dirty fossil fuels like oil and coal. The sun’s output increased slightly in the first half of the 20th century, but satellite measurements show that output has barely changed in recent decades. The variation in the sun’s energy over the course of the 20th century just isn’t significant enough to account for the rapid global warming we’re experiencing now.
• #23: Other planets are warming

  Deniers say: It's not just the Earth that's warming — what about Mars?
  Science says: We don't know if other planets are warming. We know the Earth is — and it's our own fault.
  
It’s true that the sun affects the climates of the planets in our solar system — including our planet. If the sun’s energy significantly increased, we would expect most or all of the planets to warm up. But there’s no good evidence of consistent warming on planets other than Earth. And the variation that’s occurred in the sun’s energy over the course of the 20th century just isn’t significant enough to account for the large-scale climate change we’re seeing here. Multiple lines of evidence confirm that humans, not the sun, are the primary cause of the climate change that's happening here on Earth.
• #24: It’s cosmic rays

  Deniers say: Cosmic rays from outer space seed clouds here on Earth. We’re seeing fewer cosmic rays, so we’re also seeing fewer clouds that block sunlight — that's the reason we have global warming.
  Science says: Let's get serious. Global warming has nothing to do with cosmic rays — or anything else from outer space. 


  Some scientists believe cosmic rays (high-speed particles from outer space) are one of the reasons clouds form in the Earth's lower atmosphere. Hypothetically, if fewer cosmic rays were bombarding Earth, fewer clouds would form and the planet would warm. But here’s the thing: The number of cosmic rays hasn’t changed much in recent decades, and scientists have failed to find a consistent relationship between cosmic rays and clouds. There is overwhelming evidence that the Earth has been steadily warming since the Industrial Revolution, and the reason for this warming is pollution from dirty energy like coal and gas.
• #25: It’s El Niño

  Deniers say: The El Niño Southern Oscillation (ENSO) and other similar natural cycles are the dominant causes of global warming.
  Science says: El Niño and La Niña make temperatures change from year to year. In the long run, the Earth is steadily warming.
  The climate is warming — and that means if you look at a graph of average global temperatures, you’ll see an overall upward trend over the last 130 years. But from year to year, you’ll also see the temperature wiggle up and down. Part of that wiggle comes from natural climate patterns such as El Niño and La Niña. The world tends to be slightly warmer during El Niño episodes — 1998 is a great example of that. During La Niña episodes, the world tends to be slightly cooler. Here’s the thing: Despite variations from year to year, the Earth is still warming up.
• #26: It's the Pacific Decadal Oscillation

  Deniers say: There’s a temperature pattern in the Pacific Ocean that causes warming and cooling every 20-30 years.
  Science says: The Pacific Decadal Oscillation shifts heat around the globe, but the Earth is steadily warming overall.
  The climate is warming — and that means if you look at a graph of average global temperatures, you’ll see an overall upward trend over the last 130 years. But from year to year, you’ll also see the temperature wiggle up and down. Part of that wiggle comes from natural climate patterns such as the Pacific Decadal Oscillation (PDO). The PDO cycles between warm and cool phases that typically last 20-30 years each. Here’s the thing: Internal climate cycles like the PDO primarily redistribute heat around the planet. Unlike carbon pollution, they don’t INCREASE the total amount of heat held by the oceans and the atmosphere. When you look at the long-term trend over decades, the overwhelming evidence shows that temperatures are rising and humans are to blame.
• #27: Water vapor is the most powerful greenhouse gas

  Deniers say: Water vapor is a greenhouse gas, and there’s a lot more of it in the atmosphere. So why all the focus on CO₂?
  Science says: Carbon dioxide is like a control knob on our planet's thermostat. More carbon pollution = more global warming.
  Here's what's most important: If you increase the amount of carbon pollution, the planet warms. And humans have increased the amount of carbon dioxide by about 40% by burning dirty energy. Water vapor is important, too, but the details are a little technical. As carbon dioxide traps heat and the planet warms, two important things happen: 1) More water evaporates from the oceans and land, and 2) the atmosphere retains more water (because warm air can hold more moisture than cold air). Then, since water vapor is a greenhouse gas, it causes the temperature to go up even further. Studies show that the water vapor "feedback loop" roughly doubles the warming caused by carbon dioxide.
• #28: It’s methane

  Deniers say: Methane is a much more powerful greenhouse gas than carbon dioxide.
  Science says: Does methane trap heat? Yes. But carbon dioxide has caused three times more warming than methane.
  Even though methane is better at trapping heat than carbon dioxide, there’s a lot less of it in the atmosphere. Over the last century, carbon dioxide has caused about three times more warming than methane. And sorry, we can’t duck responsibility for methane-induced warming any more than we can for carbon dioxide-induced warming. At least half of the methane in the atmosphere comes from sources like livestock (we’re not talking wild cows, here) along with coal mines and landfills.
• #29: It’s ozone depletion

  Deniers say: As the ozone layer disappears, the extra UV radiation warms the planet.
  Science says: The ozone hole has an insignificant impact on our climate. 

Carbon pollution is the main cause of global warming.
  We all know there’s a “hole” in the ozone layer — a section of the atmosphere over Antarctica where the concentration of ozone is a lot lower than it should be. But the logic that sunlight is streaming in through this hole and causing climate change just doesn’t work. Like carbon dioxide, ozone is a greenhouse gas that traps heat. So the depletion of the ozone layer actually has cooled Earth’s climate very slightly. Why are we still seeing warming then? Because we’re putting 35 billion tons of global warming pollution into the atmosphere every year.
• #30: It’s soot

  Deniers say: Carbon dioxide isn’t the main problem: It's the soot from burning coal, wood, diesel or dung.
  Science says: Soot pollution changes the climate in the short term. Carbon pollution is the main culprit over the long term. 


  The main cause of the climate change we’re seeing now is greenhouse gas pollution, which we put into the air when we burn dirty energy like oil and coal. Soot, also called "black carbon," is a contributor, too, but not to the same extent. That’s because soot only stays in the air for days to weeks. Carbon dioxide, on the other hand, has a lifetime of a century or more. Reducing soot would do a lot in the short term to help slow warming. But to protect our climate in the long term, we need to reduce greenhouse gas pollution from dirty energy.
• #31: It’s aerosols

  Deniers say: Aerosol particles reflect sunlight. There are fewer aerosols in the atmosphere now, so that's why the planet is warming.
  Science says: Aerosol pollution impacts our climate over the short term. Carbon pollution is the main culprit over the long term.
  The main cause of the climate change we’re seeing now is carbon pollution, which we put into the air when we burn dirty energy like oil and coal. But carbon dioxide and other greenhouse gases aren’t the only air pollution released by human activities. For example, the harmful haze you see and breathe in big cities like Los Angeles or Philadelphia is made of “aerosols," a name for various kinds of tiny particles in the atmosphere. Carbon pollution traps heat and causes warming, but aerosol pollution in haze reflects sunlight. This temporarily masks some of the warming we would otherwise see due to carbon pollution. Thankfully, the U.S. and many other countries around the world have worked to reduce haze-forming aerosol pollution, and we can all breathe a little easier. But this also means the slight cooling effect of aerosols is reduced, and the world is a little warmer as a result. Here's what's important: It's carbon pollution, not aerosols, that is steadily warming our planet.
• #32: It’s fewer volcanic eruptions

  Deniers say: Volcanic eruptions have decreased for the last couple hundred years, so that’s why we’re seeing warming.
  Science says: Climate change doesn't come from volcanoes. It's us.
  In the early part of the 20th century, a slowdown in volcanic activity helped warm the planet slightly. Large volcanic eruptions eject sulfur dioxide, which rapidly forms tiny particles in the air known as "aerosols" that block sunlight. So with less volcanic activity, you’d expect to see more warming. But this happened at the same time that humans were just starting to burn dirty fossil fuels in earnest. And the more fossil fuels we burned, the more carbon pollution we put in the atmosphere. Today, we’re putting about 35 billion tons of heat-trapping carbon pollution into the atmosphere every year — and that’s what’s causing most of the global warming we’re seeing today.
• #33: It’s waste heat

  Deniers say: Appliances give off heat when they're turned on, and that's the main cause of global warming.
  Science says: Waste heat from your computers isn't causing global warming — but the dirty energy powering your computer is.
  The engines, appliances and electronic devices we use release heat during operation. For instance, think about a laptop computer, which can get uncomfortably warm if you rest it on your legs for too long. That heat is often called “waste heat” because it escapes without being put to good use. So, given how many machines and devices we use — particularly in rich, industrialized countries — could waste heat be warming the planet? Not really. Waste heat is currently responsible for about 100 times less global warming than carbon dioxide and other greenhouse gases. In other words, it’s not a big problem. Not like the 35 billion tons of carbon pollution we put into the air every year when we burn dirty energy like oil and coal.
• #34: The climate has changed before

  Deniers say: The climate has changed over and over, long before humans had anything to do with it.
  Science says: Climate change doesn't just happen — it happens for a reason. And today, the reason is us.
  Has our climate changed before? Absolutely! Nobody disagrees with that. But arguing that humans aren’t the cause of climate change today is like arguing humans can’t cause forest fires because they've been started by natural causes in the past. Basic physics tells us something important: Climate change happens for a reason. Some past changes in the climate were driven by the sun burning brighter, or by an increase in volcanic activity. That’s not the case now. There is overwhelming scientific evidence that humans are causing most of today’s climate change by burning dirty fossil fuels and sending carbon pollution into the atmosphere at an unprecedented rate.
• #35: It's a 1500-year cycle

  Deniers say: Climate goes through natural cycles. The warming we’re seeing now is just part of a 1,500-year cycle.
  Science says: Some natural cycles make it warmer in one part of the world and colder in another. Man-made climate change makes it warmer everywhere.
  From ice core data we can see that on approximately 1,500-year cycles, the northern polar region has warmed while the southern polar region has cooled. This "see-saw" effect redistributes the planet’s heat, but total heat in the global system stays the same. In other words, regional temperatures change, but the average global temperature doesn’t. These regional cycles are unlike what we’re observing now. The global temperature is rising because of carbon pollution from human activities. And there’s nothing natural about that.
• #36: The Little Ice Age just ended

  Deniers say: The last 150 years of warming is just a natural recovery from the last ice age.
  Science says: A planet doesn't "recover" from an ice age like we do from hypothermia. The Earth is warming up, and carbon pollution is to blame.
  The “Little Ice Age,” the most recent cool period in the Earth’s history, may have been triggered by decades of intense volcanic activity. Scientists generally agree that the Little Ice Age ended in the late 19th century. So, could the warming we’re seeing now simply be a “recovery” after the Little Ice Age? No. Although the climate goes through cycles, there isn’t a normal recovery point. In other words, warming after an ice age isn’t like a human naturally recovering from hypothermia. Something has to force the climate to get warmer. In the early part of the 20th century, the Earth warmed because of less volcanic activity and more solar activity. But most of the warming from the mid-20th century onward has been due to carbon pollution from dirty fuels. And now, the planet is warmer than at any point in the last 1,000 years … meaning it’s warmer than well before the start of the Little Ice Age.
• #37: The Medieval Warm Period was warmer

  Deniers say: If you think it’s warm now, look back at the Medieval Warm Period.
  Science says: The so-called Medieval Warm Period was actually cooler than it is today under man-made climate change.
  When climate deniers want to change the subject away from the warm temperatures we're experiencing now, they sometimes claim it was warmer in Medieval times. First off, during the so-called "Medieval Warm Period," some regions experienced unusually warm temperatures, while others were really cold. If you average everything out, global temperatures during this period were actually COOLER than they are now. Moreover, in Medieval times, warming or cooling happened for natural reasons, and there was no significant carbon pollution to warm our atmosphere. Overwhelming evidence points to carbon pollution from dirty energy like coal and gas as the main cause of today’s climate change.
• #39: It didn’t warm during the Industrial Revolution

  Deniers say: The air was much dirtier during the Industrial Revolution. Why wasn’t there any global warming back then?
  Science says: Half the carbon pollution from humans took place after 1979. It's no surprise the world is warming up a lot faster since then.
  Since 1880, 30 years after the Industrial Revolution ended, the world has warmed nearly 1.5 degrees Fahrenheit (or 0.8 degrees Celsius). But look a little closer at the data, and you’ll see something interesting. More than half the warming has occurred since 1979. That’s not a surprise, given that more than half of the carbon pollution from human activities has also happened since the 1970s. We’re putting about 2,700 times more carbon dioxide into the atmosphere now than we were at the beginning of the Industrial Revolution. That's why the planet is warming up so much faster now than it did from 1880 to 1979.
• #58: Arctic ice melt is natural

  Deniers say: Arctic ice has melted before — it has nothing to do with climate change.
  Science says: It's not a coincidence. As carbon pollution warms the planet, Arctic ice is shrinking to record-lows.
  Has Arctic sea ice changed before? Absolutely! Nobody disagrees with that. But arguing that man-made warming isn’t melting sea ice is like arguing humans can’t cause forest fires because they've been started by natural causes in the past. The amount of summer sea ice in the Arctic has dramatically declined over the last 30 years. And the oldest, thickest ice is getting thinner. Right now, Arctic sea ice is disappearing faster than at any time in at least the last few thousand years. If this pace keeps up, the Arctic could be ice-free in summer as early as 2035.
• #63: Greenland was green

  Deniers say: The Vikings lived in Greenland a thousand years ago when it was green, but died out when the climate got colder.
  Science says: Global warming is happening right now, and the more we pollute, the worse it will get. The Vikings have nothing to do with it.
  Sure, parts of Greenland were probably greener during warmer periods of our planet’s history than they are now. But whether or not parts of Greenland were greener in the past is irrelevant to our present discussion of manmade climate change. The Earth's temperatures are increasing rapidly because of human activities. Temperatures vary around the globe, but most areas — including Greenland — are getting warmer. In fact, Greenland is losing more than 200 billion tons of ice every year. A rapidly warming climate isn't good news for Greenland or the rest of us.
• #69: Mt. Kilimanjaro's ice loss is due to land use

  Deniers say: Ice melting on Mount Kilimanjaro has local causes. So why should we believe in global climate change?
  Science says: It's not about one glacier or one mountain. Overall, glaciers are losing 150 billion tons of ice a year.
  Mount Kilimanjaro is losing snow and ice. Is this because of global warming? Maybe, but changes in local weather patterns might be more important. Conditions have become drier, meaning less snow is falling to replenish the glaciers and reflect sunlight. Researchers have found that deforestation of the mountain’s foothills is a significant contributor to this drying trend. Still, as one researcher of Kilimanjaro’s deforestation put it: “The fact that the loss of ice on Mt. Kilimanjaro cannot be used as proof of global warming does not mean that the Earth is not warming. There is ample and conclusive evidence that Earth's average temperature has increased in the past 100 years, and the decline of mid- and high-latitude glaciers is a major piece of evidence."