Most scientists agree that climate change is a real and growing threat. From rising sea levels to melting glaciers and extreme weather patterns, our environment is changing, and they believe humans are largely to blame.

But skeptics don’t agree: so-called climate change deniers argue that people have little to no impact on global climate movements. Global Ideas picked three of the most common arguments made by climate skeptics and asked researchers to pick apart the theories behind them.

Theory 1: 'Global warming stopped in 1998'

Climate change skeptic blogs are awash with the theory that that there has been no discernible warming of the earth for years – since 1998. That date is no coincidence since 1998 was a record warm year. That was largely due to El Niño, a meteorological pattern where warm ocean water temperatures spur warmer weather every few years.

Skeptics however use 1998 as evidence to argue that the resulting dip in global temperatures points to a major reversal and that global warming has effectively “stopped” since the record warm year.

But scientists who assert that greenhouses gases, produced by human activity, are the cause of modern-day climate change, point to flaws in that argument.

“If you compare summer temperatures with winter, you’ll also see a cooling pattern,“ Urs Neu, a researcher at the SwissAcademy of Sciences in Bern, says. “When you study these trends you have to take several factors into account, including natural ones,“ he says.

He argues that volcanic eruptions and weather patterns like El Niño – or the counter phenomenon, La Niña – produce largely inconclusive results. El Niño is responsible for warm ocean currents in the eastern tropical Pacific, while La Niña generates cooler sea surface temperatures. These fluctuations in the surface temperature of oceans can cause major climatic changes across the globe, from heavy rains in Peru to severe droughts in Australia.

“If you leave such factors out of the equation, you can see very well that global warming is a continuing trend,“ says Neu.

Theory 2: 'Long winters, cold summers – what global warming?'

Changing weather patterns are another issue where climate change deniers feel strengthened in their conviction that the world is not actually getting warmer.

Many point to the winters in recent years in Central Europe as an example.

Measurements by the German Meterological Service shows that winter temperatures have dropped on an average by around two degrees over the last quarter of a century. Sceptics from the European Institute for Climate and Energy have seized on the data to argue that the earth can hardly be warming in face of these falling temperatures.

It may sound paradoxical, but climate researchers say it could be exactly this development that is a result of global warming. It’s important, they say, to look beyond your own borders at the bigger picture.

Klaus Dethloff from the Alfred Wegener Institute for Polar and Marine Research says researchers have been able to prove a statistical correlation between diminishing polar ice in the Antarctic in late summer and a particularly harsh winter in Central Europe and Asia.

In other words, the trend towards rising temperatures has continued across the world, regardless of long winters and cool summers in individual regions.

Theory 3: 'Man-made climate change is minor'

A third commonly heard argument heard from climate change doubters is that carbon dioxide is not nearly as dangerous as believed, especially because nature needs the gas to function.

Scientists agree that plants do indeed require CO2 to survive, but only enough to maintain a balanced ecosystem. When that ecosystem is intact, says Urs Neu, plants only take in as much CO2 as is emitted.

”As soon as you disrupt that balance and add another source to the mix, the concentration starts to climb and so does the danger to the climate. It’s just like a bathtub: if you only fill it up with as much water as you can drain, it works fine. But if you turn the tap on at full force, at some point the water will overflow,” he says.

Economic reasons driving climate skeptics?

And these aren’t the only theories that climate change skeptics to base their arguments on. In their book „The Cold Sun,“ Fritz Vahrenholt and Sebastian Lüning, for example, argued that we’re approaching a period of decreased solar activity, which will bring a temporary end to climate change.

But that’s contradicted by scientists who at best see a marginal change in solar variations.

Carel Mohn, the press spokesperson for the European Climate Foundation, says economic reasons lie behind many of the climate doubters’ arguments.

“In industrialized countries, you have major companies that depend on extracting fossil fuels from the earth and exploiting them. Of course they have an interest in keeping that business model running as long as possible,“ he says, adding that climate skeptics in developed nations are especially powerful.

Hartmut Graßl, a climate researcher and the former director at the Max Planck Institute for Meteorology in Hamburg, says there is a political component to climate skepticism.

“Some of them even get paid, by big oil companies for example, to undermine climate change,“ he says. Graßl believes small groups, financed by big interests, are often sent to climate conferences to listen to the arguments at hand and find ways to dispute them.

Questionable theories

Scientists accuse climate skeptics of simply cherry picking the theories that suit them best, rather than accepting the entire truth.

“They dig around for results that fit their argument and then combine them to create a plausible story so that the ordinary person thinks that climate research is misleading,” Carel Mohn says. His organization’s website aims to use climate education and awareness to knock the the wind out of climate skeptics’ sails.

Hartmut Graßl says climate skepticism is primarily “charlatanism.”  He stressed that most skeptics are laypersons and  hard to find in serious scientific circles and communities.

In the scientific field, publications are subject to a system of review where content undergoes strict editing. “Ninety percent of climate skeptics don’t have the necessary references,” Graßl says. Instead, he says, they spread their unsubstantiated beliefs via blogs or media articles.

Still, Graßl says climate skeptics’ can play a positive role too – sometimes they can be helpful in kickstarting a discussion.  “But often the debates take place at a level where, as a scientist, it’s simply better to say nothing at all,” he says.