For the past several decades, climatologists have been studying the Earth's temperatures and have been growing increasingly alarmed at the rate that the planet's temperatures have been rising. According to NOAA's Isaac Held, the temperature grew by half a degree Celsius in just 25 years, starting in the mid-1970s. However, the last 15 years has seen a pause, or a hiatus, in the rate of temperature increase, and that fact has been adding fuel to the climate debate fire.
Climatologists who support the idea of global warming, and more specifically, man-made global warming, have been warning of a steady rise in global temperature and the serious implications that could have in the future, from sea-level rise swallowing coastal cities to increased severe storms. Climate change deniers see this pause in the temperature increase rate as proof that global warming is not as alarming as the other side claims, or perhaps that it is not occurring at all.
National Geographic's Dan Vergano simply explains exactly how these surface temperatures are gathered. Temperatures are taken at locations all over the world, within a meter of ocean surfaces and within a meter of land surfaces. These temperatures are then blended together to achieve a surface temperature for Earth. There are other planetary temperatures to consider, however, than just those at the surface.
"If you're talking deeper in the ocean and higher in the atmosphere, the increase is actually just going up steadily, they don't see a pause in the middle atmosphere and in ocean depths within 250-meters of the surface," Vergano told AccuWeather.com. "Things are still going up there, there's no pause there, this is a surface temperature effect."
Vergano noted that the hiatus at the surface is not occurring at the same rate across the globe. An outlying "cool spot," though not actually cool, has been affecting the overall results for the planet's temperature. In the Eastern Pacific Ocean, around the Galapagos region, the temperatures have not been rising as steadily as surface temperatures are rising in other parts of the world, which has been balancing the averages out.
"If you took that spot out where you're not seeing the heating, we'd been seeing that the heating going up everywhere else in the world," Vergano said.
Vergano explained that to scientists, it's just an expression of natural variability.
In his article "The Cause of the Pause" in the September 2013 issue of Nature, Held offers a few explanations for what could be causing the pause in terms of this variability, including "the minimum in solar energy output in the latest 11-year sunspot cycle lasted longer than usual, stratospheric water vapor, which warms the surface, has been relatively low since 2000, and the El-Nino Southern Oscillation cycle of warm El Nino and cold La Nina phases in the equatorial Pacific, which is known to affect global mean temperatures and not just temperatures of the equatorial Pacific, has favoured the La Nina phase since the major El Nino event of 1997-98."
Essentially, that naturally changing systems such as the weather and fluctuations in the atmosphere and in the ocean, could be accounting for some of the outlying regions that are skewing the overall numbers.
"In the Pacific there's this El Nino/La Nina pattern, that goes on a decade scale, and what you see is that it reoccurs," Vergano said. "Here we're having this really extended La Nina-like effect going on in the Eastern Pacific, which leads to cooling of the surface water in the Pacific, and if you through that extra cooling in your line of numbers for all these temperature readings and it balancing out to look like not a lot of increased warming at the surface of the globe."
Those in the climate change camp also point out that temperatures were never expected to rise in a straight line over the course of time, and that though this pause is somewhat longer, it's not the first temperature rise hiatus that has been observed.
"It keeps going up over 30 years, over 40 years, over 50 years, you look at it and say 'yeah, it's gone up,' but it's jaggedity, the increase, it's not a roller coaster ride straight up the hill," Vergano explained.
Overall, he said, the rise is still on track with past predictions.
"The other thing to keep in mind is that it's still warm. The temperatures are stuck way up there, it's not like global warming has just stopped," Vergano said. "It's way warmer than it was in the middle of the 20th century."
Some have questioned why more of these reports were not addressed in the latest Intergovernmental Panel on Climate Change release. Vergano pointed out that some of the latest studies on this topic came out this past August, too late to be included in the latest report from the IPCC.
For climate change deniers the pause in global warming is explained more simply; that the change just isn't happening.