Why "slowed" global warming is not what it seems

Thirteen of the 14 hottest years on record have all occurred since 2000, and yet there have recently been new claims that global warming “has stopped.”

Most recently, a Wall Street Journal guest columnist caused a stir when he argued that urgent climate action may not be needed, after all. So what’s going on?

Well, climate change hasn’t stalled, but the rate of change has been slower for the last 15 years than in previous decades. With the United Nations’ Climate Summit just around the corner on September 23, it’s no surprise that claims of a climate “hiatus” are raising eye brows.

Consider these four key factors:

Different things drive the rate of global warming. Researcher have dug deeply into the science underlying many processes critical to the slowing of the increase in global temperatures over the past 15 years. They found that natural ocean cycles and small volcanic eruptions have played an important role. While ever-growing emissions are driving climate change, there are other factors that affect the rate of temperature increase as well.

New evidence may set the record straight. There is evidence that the temperature records downplay the warming rate because they are missing key data from hard-to-access locations in the Arctic and Africa – which are warming at a considerably faster pace than the global average. Weather stations are sparse at the poles and in deserts, and patchy measurements of temperature on a global scale can influence temperature records. When more advanced techniques are deployed to fill data gaps, the pattern shows that the pace of warming has, in fact, not slowed.

Oceans continue to build up heat. Only 2 percent of the trapped heat actually affects the atmosphere; 90 percent ends up in the ocean. While the prominent surface air temperature records show that the rate of global warming appears to have slowed down, the deep ocean continues to acquire more and more energy. Because the heat capacity of the ocean is so large, it takes a lot more energy to raise the ocean’s temperature by a degree than it takes to heat the atmosphere. So the massive amount of energy that is accumulating in the ocean is not as obvious.

The climate system is incredibly dynamic. Countless interconnected processes occur simultaneously. This is why it’s taken half a century, and thousands upon thousands of scientists working to challenge and test what is happening across the world - and why it’s taken millions of hours of supercomputing time to understand what the future will be like if we don’t curb emissions of heat-trapping gases.

Time to broaden our climate lense

There is a misconception that average surface air temperatures are the sole indicator of climate change.

Rather, the climate doesn’t care how we decide to interpret the global surface temperature records from human measurements – the climate is just responding to what is, in fact, happening.

Those responses are visibly noticeable and accelerating. Consider:

• melting glaciers, snowcaps, ice sheets, and permafrost (in both Siberia and Canada). sea levels that are rising faster than anything in the past two millennia.
• an ocean that is 38-percent more acidic than before the Industrial Revolution.
• hurricanes that are shifting their tracks and intensity.
• increased heavy rainfall episodes.
• amplified droughts.

So while the increase in surface air temperatures has seemingly slowed, the impacts of global warming have not.

Thus, the lens through which we perceive climate change has to be broader than a single temperature metric to give us a comprehensive view of the processes that matter. This will, in turn, provide a better diagnosis of the things we care most about - such as agricultural production, extreme weather and human health.

Taking a holistic look at the entire climate system, it’s clear that urgent action is needed now.