Global warming is a hot topic and has been for the last few decades. It became more serious with the Kyoto Protocol which was adopted in 1997, where 191 countries agreed to limit and reduce their emission of greenhouse gases. And then the carbon credit was invented, where each country would have a specific number of credits to use in terms of carbon emissions. And a stock market exchange started where companies and countries would sell and buy carbon credits. Which makes you wonder if all of this was again just a money game from which many were profiting.
Professor Alfred P. Sloan of MIT in a recent article suggested that the scientists supporting global warming in an alarming way get funds and support, while any scientist with a different opinion is intimidated, sees their grant funds disappear, their work diminished and even lose their position. We do not say that the emission levels of CO2 haven’t increase, we say that the increase doesn’t constitute a global warming and doesn’t justify the alarming attitude that is created. So again is money the motivation or fear of the global warming movement?
Recently a draft of a U.N. climate change report was leaked showing that all temperature models the United Nations used from 1990 to 2012 overestimated the warming of the earth during that time.
The conclusions are yours.
Climate scientists debunk 13 myths about global warming
Deepti Singh: It's not by their farts, but it's by belching.
Cook: "A few degrees' difference is not a big deal." And the way I always like to think about it too is like your body's temperature. If your temperature is three or four degrees warmer, then you're seriously sick.
"It's too late to do anything about it." Unless you're Elon Musk and gonna head off towards Mars, we're all stuck here, so we should try to figure out how we can make it the best planet we can.
Singh: I'm Deepti Singh. I'm an assistant professor in the School of the Environment at Washington State University. I've been studying climate change for about 11 years, and I study extreme weather events and how human activities are influencing them.
Cook: My name is Benjamin Cook, and I'm a climate scientist at the NASA Goddard Institute for Space Studies. I've been working there for about 14 years now. And I study how droughts are changing with global warming and climate change.
Singh: And today we'll be debunking myths about global warming.
Cook: Myths from pop culture. Oh, boy, I'm glad you got this one, Deepti. "The sun is causing global warming."
Singh: Changes in the amount of energy we get from the sun do affect our climate. But over the last 150 years, we know that because the amount of energy we're getting from the sun has not changed significantly over this period. Satellites have been recording the amount of solar radiation that our planet receives. I think Ben has a graph that shows that.
Cook: And what we're looking at here on the yellow is the amount of energy that's coming from the sun, and red is global temperatures. It's pretty clear that the amount of energy we're getting from the sun has been more or less flat for the last several decades, even as temperatures continue to go up and up.
Singh: "Scientists don't agree on what causes climate change."
Cook: 100% of the climate scientists on this Skype call agree.
Singh: If you review the published literature in reputable journals by reputable scientists, all those papers agree that climate change is caused by human activities.
Cook: There's really no other explanation that fits the data. We've looked at the sun. We've looked at just natural variations in circulation in the ocean, in the atmosphere. We've looked at volcanoes. We've looked at changes in ecosystems. And at the end of the day, the only thing that can adequately explain the degree of warming that we've seen over the last 150 years is human greenhouse gas emissions, primarily through the burning of fossil fuels. There's a real clear incentive for people to find some other explanation. Nobody can come up with even a plausible alternative hypothesis.
"Global warming is caused by cow farts."
Singh: It's not by their farts, but it's by belching. Agriculture is a pretty substantial contributor to greenhouse gas emissions, close to 25%. It's not the whole 25%, but it's a good chunk.
Cook: It's important to note, too, that even the cow burps that are producing this methane is not natural. It's all part of a kind of human agricultural system. So blaming it all on cows doesn't take people off the hook.
Singh: "Plants and animals will adapt."
Cook: So, we know that in the past, plants and animals have adapted to climate change, but there's a few fundamental different things now that are very likely to make it quite difficult. In addition, it's not just climate change that's threatening plants and animals, it's habitat fragmentation, it's pollution, it's a variety of other environmental stressors. And so once you kind of put climate change on top of pollution, on top of habitat loss, then it becomes much, much more difficult.
Singh: And just to add to that, I think the extinction rate of species is much higher than the natural extinction rate. And it's partly driven by the processes that Ben just mentioned.
Cook: Myths from social media.
Singh: "Global warming is natural."
Cook: So, we know in the past that climate can change really dramatically from natural causes. The climate during the time of the dinosaurs is very different from the climate during the time of the last ice age. But the changes that we're seeing right now for the most part are not natural. The warming that we're seeing is very likely the fastest warming we've seen anytime in the last several thousand years. It coincides directly with the industrial revolution and the burning of fossil fuels and widespread deforestation. You can look at almost any natural cause, and none of them are sufficient to explain the warming that we've seen in recent decades.
Singh: "Carbon dioxide is the problem."
So, CO2 isn't the problem. It's the increase in the concentration of CO2 in the atmosphere that is resulting in the rapid warming we're seeing over the last century, which is the problem.
Cook: So, carbon dioxide is one of these gases that we call greenhouse gases, because they're responsible for the greenhouse effect, which basically helps trap energy on Earth and make things much, much warmer than it otherwise would have been. It's not a big stretch then to observe that if we start increasing CO2 concentrations, we're gonna trap more energy and we're gonna warm up.
Singh: Before the industrial revolution, CO2 levels were close to, like, 280 parts per million. And now we're at close to 418 parts per million. So that's a pretty large change in the concentration.
Cook: And the fact is that pretty much anytime the world was warmer, CO2 levels in the atmosphere were higher. And anytime the world was cooler, CO2 concentrations were lower.
"A few degrees' difference is not a big deal." And the way I always like to think about it too is like your body's temperature. We're all supposed to be about 98.6 degrees Fahrenheit. Even one degree or two degrees of warming is considered a low-grade fever. And if your temperature is three or four degrees warmer, then you're seriously sick.
Singh: So, just to give you a sense, the Earth has warmed by about one degree over the last century. That one degree is an average temperature around our planet. That means some parts of our planet are warming faster than others. I come from India. We have a lot of people that live below poverty in the country. And most of those people, for example, don't have an air conditioner to deal with extreme heat events. So it depends on who we're talking about when we say it's not a big deal, because there are some people around the planet that have the capacity to adapt or cope with these kind of extreme events and with the warming that we've experienced, and then there are billions of people that do not have the capacity to cope with even small changes.
Myths that we, climate scientists, hear the most.
"Global warming will destroy the planet by 2030."
Cook: Just like there's kind of climate deniers who don't know what they're talking about, there's climate doomists who also don't know what they're talking about. This whole idea of the planet being destroyed by 2030 comes out of discussion about, how much time do we have to keep global warming under two degrees? And so it's very likely that we need to kind of get emissions under control by 2030 to keep it under two degrees. It doesn't mean that the world is going to explode or we're all going to be consigned to a fiery "Mad Max" kind of hellscape. It just means that it'll be warmer than we maybe wanted it to be.
Singh: When they say it's gonna destroy the planet, well, the planet's not going to blow up. But it does mean that the way of life and the livelihoods and the things people depend on are going to be affected. There are already people who have been displaced because of sea-level rise, people that are experiencing life-threatening heat conditions.
Cook: The impacts of climate change are not going to be equally felt. These kind of blanket statements are very, very dismissive. And I think they can take attention away from the people who are likely to be most vulnerable to climate change.
Singh: It's not really helpful to put a date on it. I think we just need to know that delaying action on climate change is going to just cost more to society.
Cook: "Global warming is China's fault."
Singh: So, to address that myth, I think there's one important fact we need to understand. When CO2 is emitted, it can stay in the atmosphere for hundreds, if not thousands of years. The CO2 concentrations we're seeing today are a consequence of emissions that have happened over a much longer period, over the last century. And most of those emissions are associated with the industrial revolution and development of countries like the US and industrialized nations in Europe. If we look at emissions this year specifically, sure, the emissions from China are close to what the emissions from the US are. But those emissions are being used to produce products and goods that are being used in other parts of the world. So I don't think it's fair to say that China's responsible when we're all benefiting from the products that are produced there.
Cook: I think even today, it's worth thinking not just about how much is a country emitting, but how much are they emitting per person? And I have another visual aid here. You can pretty clearly see the highest-intensity emitters are places like Australia, the US, Canada, Russia, Saudi Arabia. China isn't even in the top 10.
Singh: It's also a complicated problem because the well-being of people is tied to their consumption of energy. So as long as we're doing that in a sustainable, cleaner way, I think we all have to benefit from it.
"Renewable energy is too expensive to be realistic."
Cook: Renewable energy is getting cheaper all the time, even faster than we expected. And there's a lot of places where it actually can outcompete some fossil fuel sources. For example, I believe wind and solar is more cost-effective than coal in pretty much the entire United States.
Singh: The cost of producing solar panels today is a fraction of what it was just a decade ago. I keep going back to India because that's another region I'm very familiar with. There are a lot of villages there that have been provided energy because they're using solar and wind, which would not have been possible if we were still depending upon CO2. Now, there's still challenges.
Cook: We're not going to kind of be able to switch everything overnight, but it's like any other technology. It's getting cheaper over time. It's getting more efficient. And the more we kind of invest in it, then the faster we'll get to the point that we'll be able to use it for most of our needs.
"Extreme weather isn't caused by global warming."
Singh: So, the right question to ask is not whether an extreme event would have been possible without warming, but it's to ask how the event itself was affected by warming. For example, a tropical storm or a tropical cyclone might result in heavier precipitation because a warmer atmosphere holds more moisture. And so there's more moisture, more fuel in the storm, which results in heavier precipitation and likely more flooding.
Cook: I think a good analogy is a professional athlete on steroids. Athletes need to have some kind of innate fitness and ability, but if you go on steroids, you're a bit more likely to hit a home run. So CO2 is kind of like the steroids of the climate system, and it's just intensifying everything that's already there.
Singh: "The temperature record is unreliable." What do you have to say about that, Ben?
Cook: The record we have of warming for the last 150 years is constructed from basically thousands of thermometer records from around the world. Climate scientists often get accused of modifying the temperature record to make it look like it's warming more than it actually is. At least half a dozen groups around the world who are all independently putting together these records and estimating the global temperature changes that we've seen over the last two centuries, and they're all basically getting the same answer. All this data is publicly available! Anybody can go and get this data and come up with their own calculation. And the fact is that nobody has shown one that is credibly different.
"It's too late to do anything about it."
Singh: It's easy for us to say, "Well, it's too late to do anything about it. Let's throw our hands up and not do anything about it." But there is a lot we can do about it, both individually as well as at the international level. It doesn't have to be a major change, but reducing our consumption of certain meat products that are extremely energy-intensive is one way in which we can affect greenhouse emissions.
Cook: The decisions we make today, we are going to have to deal with, our children are going to have to live with. I will never say that people should not recycle or reduce their car use or eat less meat. But at the end of the day, the big lever is just going to be government. And 'cause the government can set policies that can incentivize actions.
Singh: It's also a weird time to say that it's too late to do anything about it, because we're at a point in time when we have so much information. There are people working on technologies to address climate change and to make our environment cleaner and better. So this is not a time for us to put our hands up. It's our time to take action.
Cook: Climate change itself is not pass-fail. Keeping warming to three degrees is better than four degrees. Keeping warming to two and a half degrees is better than three degrees. Keeping warming to two degrees is better than all of those things. We're all stuck here, so we should try to figure out how we can make it the best planet we can. Climate change is a global problem, and it's going to require a global solution and people to actually kind of work together.
Myth No. 4: There have been big climate changes in the past, such as the Little Ice Age and the Medieval Warm Period, so why can’t recent climate changes just be explained by natural variability?
People who dispute evidence of recent global warming sometimes point to two episodes in the past 1,000 years called the Little Ice Age and the Medieval Warm Period — times when northern hemisphere temperatures were higher or lower than average for decades or even centuries — as examples of internal variability, a kind of natural randomness in the climate system that can’t be explained by any specific forcing. If true, perhaps internal variability could explain the current rapid global warming, skeptics argue. In other words, maybe our current warming is just an unlucky roll of the dice, a blip rather than a long term trend.
Continue reading this myth …
The Greenhouse Effect
In the 1820s, French mathematician and physicist Joseph Fourier proposed that energy reaching the planet as sunlight must be balanced by energy returning to space since heated surfaces emit radiation. But some of that energy, he reasoned, must be held within the atmosphere and not return to space, keeping Earth warm.
He proposed that Earth’s thin covering of air—its atmospherets the way a glass greenhouse would. Energy enters through the glass walls, but is then trapped inside, much like a warm greenhouse.
Experts have since pointed out that the greenhouse analogy was an oversimplification, since outgoing infrared radiation isn’t exactly trapped by Earth’s atmosphere but absorbed. The more greenhouse gases there are, the more energy is kept within Earth’s atmosphere.
We are the reason
Several factors affect how much of the sun's energy reaches Earth's surface and how much of that energy gets absorbed. Those include greenhouse gases, particles in the atmosphere (from volcanic eruptions, for example), and changes in energy coming from the sun itself.
Climate models are designed to take such factors into account. For example, models have found that changes in solar irradiance and volcanic aerosols have contributed only about two percent of the recent warming effect over 250 years. The balance comes from greenhouse gases and other human-caused factors, such as land-use changes.
The speed and duration of this recent warming is remarkable as well. Volcanic eruptions, as an example, emit particles that temporarily cool the Earth's surface. But they have no lasting effect beyond a few years. Events like El Niño also work on fairly short and predictable cycles. On the other hand, the types of global temperature fluctuations that have contributed to ice ages occur on cycles of hundreds of thousands of years.
The answer to the question, “Is global warming real?” is yes: Nothing other than the rapid rise of greenhouse gas emissions from human activity can fully explain the dramatic and relatively recent rise in global average temperatures.
Global Conservatives and the Myth of a Climate Change Debate
On Saturday, the Canadian Conservative Party voted down a recent proposal for the party to become more green-friendly, rejecting stances such as “Canadian businesses classified as highly polluting need to take more responsibility” and “climate change is real.”
Conservative Leader Erin O’Toole was seen Friday urging his colleagues to be more open-minded, believing that the party’s failure to recognize the scientific consensus behind human-caused climate change would hurt their chances to challenge the Liberal Party coalition and Prime Minister Justin Trudeau in the next election. But the 54 to 46 percent vote is the latest affirmation of the enduring conservative trend to reject modern climate realities.
The Canadian decision is the latest development in a much larger problem. Conservatives across the globe are continuing to rally behind a scientifically debunked claim that climate change isn’t happening. In the United States, conservative politicians — none of whom are scientists themselves — discredit and question prominent and reliable climate change researchers. In Germany, right-wing party officials pass out scientifically inaccurate pamphlets at student activist rallies.
If conservatives don’t get up to speed soon, they risk slipping further into the irrelevance of their old ways.
The “debate” over climate change is a myth that conservative leaders must cease to perpetuate. Overwhelming scientific consensus affirms that the earth is warming at historic rates. Claims to the contrary are not a valid political opinion — they are an alternate reality that is incompatible with basic fact.
The conservative talking point that recognizes rising atmospheric CO2 but rejects strong human influence on that rise is also factually incorrect.
Groundbreaking studies on historic atmospheric carbon levels found that over the past 800,000 years, carbon dioxide in our atmosphere has never surpassed around 300 parts per million, even in Earth’s warmest periods. However, since 1950, CO2 levels have risen dramatically to over 400 ppm, levels never before reached in observable history.
What’s more is that we can directly link almost all of the additional carbon production to human activities like fossil fuel consumption. And this increase is having immediate impacts on our daily lives.
In recent years, those impacts have looked like rising temperatures year over year, with increasingly unreliable weather and climate models. Data collected over the past four decades shows that between 2013 and 2019, not a single day passed where global temperatures didn’t significantly surpass historical averages. And that’s old data — a child under 8 years old today has likely not experienced a day unaffected by climate change in their lifetime.
The time to deny humanity’s role in our warming earth is long over, and conservative leaders who continue to perpetuate the myth of a debate are lying to themselves and their constituents. This is different from a debate around which policies provide the best pathway forward. Countries like France, Germany, Indonesia, Saudi Arabia, and the U.S. — with large populations that continue to subscribe to the anti-climate-change narrative — should put tax dollars to use by discussing action, not by trying to ignore extensive scientific evidence.
Not only is it bad form to oppose basic scientific fact — it’s also bad politics. While it should be clear that climate change is a problem, there is not a broad consensus on what policy will produce the best action. Politicians should be debating and working together to find the best solutions to this very real threat, not wasting time denying basic scientific fact.
In the United States, conservative climate positions detract from the right’s political credibility and inhibit its ability to push other policy priorities. Polls from recent yearsnot incompatible with conservative values. Energy independence, job creation, agricultural prosperity, and market-led innovation are all historic priorities of conservatives in the U.S. and abroad. If conservative leaders participate in conversations on climate change action, they can help shape policies that center these priorities and produce positive economic and social outcomes for their citizens.
But they can only do this by first recognizing climate change’s existence. Canadian Opposition Leader O’Toole is right conservatives “cannot ignore the reality of climate change” if they want to remain politically relevant. Conservative leaders across the globe must leave the myth of a climate change debate behind or risk getting lost in the past themselves.
After this deep freeze, there were several “hothouse earth” periods when the temperature exceeded those we experience today. The warmest was probably the Paleocene-Eocene Thermal Maximum (PETM), which peaked about 55 million years ago. Global temperatures during this event may have warmed by 5°C to 8°C within a few thousand years, with the Arctic Ocean reaching a subtropical 23°C. Mass extinctions resulted.
The warming, which lasted 200,000 years, was caused by the release of massive amounts of methane or CO2. It was thought to have come from the thawing of methane clathrates in deep ocean sediments, but the latest theory is that it was caused by a massive volcanic eruption that heated up coal deposits. In other words, the PETM is an example of catastrophic global warming triggered by the build-up of greenhouse gases in the atmosphere.
Since then, the Earth has cooled. For the past million years or so, the climate has switched between ice ages and warmer interglacial periods with temperatures similar to those of the past few millennia. These periodic changes seem to be triggered by oscillations in the planet’s orbit and inclination that alter the amount of solar radiation reaching Earth.
However, it is clear that the orbital changes alone would not have produced large temperature changes and that there must have been some kind of feedback effect (see the section on Milankovitch cycles in this article).
The Global Warming Myth?
Instead of panicking over climate change, we should adjust to it.
April 20, 2007 -- The heavy breathing over global warming is enough to terrify anyone.
Last week the Washington Post interviewed a 9-year-old who said the Earth is "just starting to fade away." In 20 years there will be "no oxygen" he said, and he'll be dead. The Post went on to say that "for many children and young adults, global warming is…defining their generation." How sad.
Thirty-six years of consumer reporting have taught me to be skeptical of environmental scares. Much of what the media scares us about turns out to be myths.
Watch "Myths, Lies and Downright Stupidity" on a special edition of "20/20" Friday, May 4th at 10 p.m. EDT
But is the global warming crisis a myth? Read on.
Excerpts from "Myth, Lies, and Downright Stupidity," coming out in paperback May 1. (Click here to buy "Myths, Lies and Downright Stupidity").
MYTH: Global warming will cause huge disruptions in climate, more storms, and the coasts will flood! America must sign the Kyoto Treaty!
This has to be broken into four pieces.
MYTH No. 1: The Earth is warming!
TRUTH: The Earth is warming. The Intergovernmental Panel on Climate Change (IPCC) said the global average surface temperature increased about 0.6 degrees Celsius over the 20th century.
MYTH No. 2: The Earth is warming because of us!
TRUTH: Maybe. The frantic media suggest it's all about us. But the IPCC only said it is likely that we have increased the warming.
Our climate has always undergone changes. Greenland was named Greenland because its coasts used to be very green. It's presumptuous to think humans' impact matters so much in comparison to the frightening geologic history of the earth. And who is to say that last year's temperature is the perfect optimum? Warmer may be better! More people die in cold waves than heat waves.
MYTH No. 3: There will be storms, flooded coasts and huge disruptions in climate!
TRUTH: There are always storms and floods. Will there be much bigger disruptions in climate? Probably not.
Schoolchildren I've interviewed were convinced that America is "dying" in a sea of pollution and that "cities will soon be under water!"
Lawyers from the Natural Resources Defense Council (another environmental group with more lawyers than scientists) warn that "sea levels will rise, flooding coastal areas. Heat waves will be more frequent and more intense. Droughts and wildfires will occur more often."
But many scientists laugh at the panic.
Dr. John Christy, professor of Atmospheric Science at the University of Alabama at Huntsville said: "I remember as a college student at the first Earth Day being told it was a certainty that by the year 2000, the world would be starving and out of energy. Such doomsday prophecies grabbed headlines, but have proven to be completely false." "Similar pronouncements today about catastrophes due to human-induced climate change," he continued, "sound all too familiar and all too exaggerated to me as someone who actually produces and analyzes climate information."
The media, of course, like the exaggerated claims. Most are based on computer models that purport to predict future climates. But computer models are lousy at predicting climate because water vapor and cloud effects cause changes that computers fail to predict. In the mid-1970s, computer models told us we should prepare for global cooling.
Scientists tell reporters that computer models should "be viewed with great skepticism." Well, why aren't they?
The fundamentalist doom mongers also ignore scientists who say the effects of global warming may be benign. Harvard astrophysicist Sallie Baliunas said added CO2 in the atmosphere may actually benefit the world because more CO2 helps plants grow. Warmer winters would give farmers a longer harvest season, and might end the droughts in the Sahara Desert.
Why don't we hear about this part of the global warming argument? "It's the money!" said Dr. Baliunas. "Twenty-five billion dollars in government funding has been spent since 1990 to research global warming. If scientists and researchers were coming out releasing reports that global warming has little to do with man, and most to do with just how the planet works, there wouldn't be as much money to study it."
MYTH No. 4: Signing the Kyoto Treaty would stop the warming.
In 1997, the United Nations met in Kyoto, Japan, and asked the developed nations of the world to cut CO2 emission to below 1990 levels.
And even advocates of Kyoto admit that if all the nations signed the Kyoto agreement and obeyed it, global temperatures would still increase. The difference by 2050 would be less than a tenth of a degree. The fuss over Kyoto is absurd. Even if Kyoto would have an impact, do you think all the signers are going to honor what they signed? China is predicted to out-emit us in five to 10 years. India will soon follow. What incentive do they have to stop burning fossil fuels? Get the shovel.
The fundamentalist greens imply if we just conserved energy, and switched from fossil fuels to wind and solar power (they rarely mention nuclear power -- the most practical alternative), we would live in a nonglobal-warming fairyland of happiness. But their proposals are hopelessly impractical. Building solar panels burns energy, as does trucking them and installing them. Not to mention taking them down again to repair them.
To think that solar energy could stop the predicted temperature increase is nonsensical. EPCOT, a theme park with a solar energy ride, consumes about 395,000 kilowatt-hours per day. The Department of Energy says you'd need around a thousand acres of solar panels to generate that much electricity. EPCOT itself only sits on 300 acres, so you'd have to triple the size of the park just to operate it. (Windmills are no panacea either. They are giant bird-killing Cuisinarts, and we'd have to build lots of them to produce significant energy.)
In 2000, a group called Cape Wind proposed to erect 130 windmills in Nantucket Sound, off the coast of Massachusetts. I think the drawings make them look interesting, but -- horrors! -- they would be visible from the Kennedy family vacation compound in Hyannis Port. Robert Kennedy Jr., grand poo-bah of the environmental zealotry movement, is leading a campaign to ban the windmills from Nantucket Sound. The group he leads, the Waterkeeper Alliance, said it supports wind farms -- but Kennedy fights the one near his home. What a hypocrite.
Eighty percent of the world's energy comes from fossil fuels. Kyoto would decimate just about every Third World country's economy, and deliver a catastrophic blow to our own.
So what should we do about the threat of global warming?
Second, if the world is warming, it is much more reasonable to adjust to it, rather than try to stop it. If sea levels rise, we can build dykes and move back from the coasts. It worked for Holland.
Farmers can plant different crops or move north. Russian farmers farmed northern Siberia for centuries. When the area became cold and desolate, the farmers moved south.
Far better to keep studying global warming, let the science develop and adjust to it if it happens, rather than wreck life as we know it by trying to stop it.
The warm period became known as the Medieval Warm Period, and the cold period was called the Little Ice Age (LIA). However, that view was questioned by other researchers the IPCC First Assessment Report of 1990 discussed the "Medieval Warm Period around 1000 AD (which may not have been global) and the Little Ice Age which ended only in the middle to late nineteenth century." It said temperatures in the "late tenth to early thirteenth centuries (about AD 950-1250) appear to have been exceptionally warm in western Europe, Iceland and Greenland".  The IPCC Third Assessment Report from 2001 summarized newer research: "evidence does not support globally synchronous periods of anomalous cold or warmth over this time frame, and the conventional terms of 'Little Ice Age' and 'Medieval Warm Period' are chiefly documented in describing northern hemisphere trends in hemispheric or global mean temperature changes in past centuries."  Global temperature records taken from ice cores, tree rings, and lake deposits, have shown that the Earth may have been slightly cooler globally (by 0.03 °C) than in the early and mid-20th century.  
Palaeoclimatologists developing region-specific climate reconstructions of past centuries conventionally label their coldest interval as "LIA" and their warmest interval as the "MWP."   Others follow the convention, and when a significant climate event is found in the "LIA" or "MWP" time frames, they associate their events to the period. Some "MWP" events are thus wet events or cold events rather than strictly warm events, particularly in central Antarctica, where climate patterns opposite to the North Atlantic area have been noticed.
A 2009 study by Michael E. Mann et al., examining spatial patterns of surface temperatures shown in multi-proxy reconstructions finds that the Medieval Warm Period, shows "warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally."  Their reconstruction of the pattern is characterised by warmth over a large part of the North Atlantic Ocean, Southern Greenland, the Eurasian Arctic, and parts of North America which appears to substantially exceed that of the late 20th century (1961–1990) baseline and is comparable or exceeds that of the past decade or two in some regions. Certain regions, such as central Eurasia, northwestern North America, and (with less confidence) parts of the South Atlantic, exhibit anomalous coolness.
In 2013, a study by the Pages-2k consortium suggests the warming was not globally synchronous: "Our regional temperature reconstructions also show little evidence for globally synchronized multi-decadal shifts that would mark well-defined worldwide MWP and LIA intervals. Instead, the specific timing of peak warm and cold intervals varies regionally, with multi-decadal variability resulting in regionally specific temperature departures from an underlying global cooling trend."  In direct contrast to these findings, a 2013 study recreated a "temperature record of western equatorial Pacific subsurface and intermediate water masses over the past 10,000 years that shows that heat content varied in step with both Northern and Southern high-latitude oceans. The findings support the view that the Holocene Thermal Maximum, the Medieval Warm Period, and the Little Ice Age were global events, and they provide a long-term perspective for evaluating the role of ocean heat content in various warming scenarios for the future." 
In 2019, using an extended proxy data set,  the Pages-2k consortium confirmed that the Medieval Climate Anomaly was not a globally synchronous event. The warmest 51-year period within 'Medieval Warm Period' did not occur at the same time for different regions. They argue for a regional instead of global framing of climate variability in the preindustrial Common Era to aid understanding. 
The Earth is warming up, and humans are at least partially to blame. The causes, effects, and complexities of global warming are important to understand so that we can fight for the health of our planet.
Earth Science, Climatology
Tennessee Power Plant
Ash spews from a coal-fueled power plant in New Johnsonville, Tennessee.
Photograph by Emory Kristof / National Geographic
Global warming is the long-term warming of the planet&rsquos overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels. As the human population has increased, so has the volume of fossil fuels burned. Fossil fuels include coal, oil, and natural gas, and burning them causes what is known as the &ldquogreenhouse effect&rdquo in Earth&rsquos atmosphere.
The greenhouse effect is when the Sun&rsquos rays penetrate the atmosphere, but when that heat is reflected off the surface cannot escape back into space. Gases produced by the burning of fossil fuels prevent the heat from leaving the atmosphere. These greenhouse gasses are carbon dioxide, chlorofluorocarbons, water vapor, methane, and nitrous oxide. The excess heat in the atmosphere has caused the average global temperature to rise overtime, otherwise known as global warming.
Global warming has presented another issue called climate change. Sometimes these phrases are used interchangeably, however, they are different. Climate change refers to changes in weather patterns and growing seasons around the world. It also refers to sea level rise caused by the expansion of warmer seas and melting ice sheets and glaciers. Global warming causes climate change, which poses a serious threat to life on earth in the forms of widespread flooding and extreme weather. Scientists continue to study global warming and its impact on Earth.