After an uncomfortable heat wave enveloped much of the Midwest and Northeast from about July 14 to July 20, there has been a renewed focus on the conversation around global warming and man-made climate change. While some make the argument that the hot summer and recent global temperatures are proof that our planet is changing, others are not so convinced.
AccuWeather.com Senior Expert Meteorologist Bernie Rayno does not dispute that humans may be impacting temperatures. Rayno said that building up in cities has increased temperatures in those areas, a phenomenon known as the urban heat island effect. He disagrees, however, that human activity is causing drastic changes to the climate on a global scale or that heat waves can be blamed on it.
"This is the time of year for heat waves," Rayno said. "Mid-July to mid-August. I'd be more concerned if we weren't seeing heat waves right now."
Rayno also emphasized that this most recent heat wave is nothing historic or out of the ordinary. What made the recent rash of heat seem so unpleasant was high humidity, not necessarily high temperatures.
"Everyone is putting more of an emphasis on heat indices instead of actual temperatures," Rayno said. "Most of the week [of the heat wave] we weren't seeing a lot of records broken for high temperatures. It was not a historic heat wave."
Though temperatures in some cities set new records, most were unusually high nighttime low temperatures. Raleigh, for example, broke the old warm-night record of 73 degrees set in 1925 when it hit 75 on July 16. The old record itself showed, however, that periods of high overnight temperatures are not entirely new experiences. Washington, D.C., had several consecutive days where temperatures failed to drop below 80 degrees.
Overall for this summer, however, temperatures have not been ordinarily hot. On the contrary, as of July 22, Washington, D.C., has only had 20 days over 90 degrees. During an average summer, the city will experience 36 days that hit 90 degrees or more. Philadelphia has had 19 days in the 90s so far this summer compared to their average of 27 days. Though the summer is not yet over, trends show that high temperatures for these areas are on track to end up near typical averages.
While many climate scientists agree that no one particular heat wave can be blamed on a changing climate, they contend that an increasing pattern over time has indicated weather is being affected by global warming.
Martin Tingley, a climatologist at Harvard University, told Ker Than of National Geographic, "Can we attribute this particular heat wave to an anthropogenic impact on the climate? The only safe answer is, well, probably not... But what we're seeing now, there seems to be a trend toward more hot extremes and fewer cold extremes. That's a pattern that's consistent with an anthropogenically-forced increase in temperatures."
Rayno points out that the planet has seen these sort of fluctuations before, citing the medieval warming period, where research has shown that the planet warmed significantly from the ninth to 13th centuries, then cooled for the "Little Ice Age" from the 15th to 19th centuries.
Though recent heat has been a focus in the debate, other extreme weather events are often at the heart of the global discussion as well. A major hurricane formed then hit New York and New Jersey in the fall of 2012 in the form of Superstorm Sandy, an EF-5 tornado struck Moore, Okla., and areas of excessive drought in the West have all been the topics of discussion in the climate debate.
Rayno does not deny that human actions can contribute to the climate but states that blaming current weather events, from Sandy to droughts to the heat wave, is "absurd."
"We live on a planet where extreme weather is not the exception; it's the rule," Rayno said. "Talking about events that have happened in the past few decades, temperature records that have only been kept for a little over a hundred years, you are only looking at a fraction of time when you consider how old the Earth is."
Rayno also believes that emphasis on recent weather extremes does not take into account the changes that have been made in the way weather events are tracked and measured. The scale used for tornadoes, for example, has evolved, making it seem as if there has been an increased number of severe tornadoes taking place, when they have actually not increased in number of tornadoes or in severity. Tornadoes are now given higher ratings with lower wind speeds.
The May 2007 Greensburg, Kan., tornado, for example, was labeled an EF-5 with estimated winds of 205 mph. Had this tornado occurred before the enhanced measurement scale was put into effect, it would have only been an F-3.
Dr. Michael Mann, professor of meteorology and the director of the Earth System Science Center at the Pennsylvania State University, disagrees, stating, "Scientists at NOAA have spent decades carefully accounting for any changes in instrumentation, etc., and the [Global Historical Climatology Network] data of NOAA are considered the gold standard for quality-assured long-term climate data."
Dr. Mann said that this data supports an increase in extreme weather, from heavy rainfall to hurricanes, a point also made in the Intergovernmental Panel on Climate Change (IPCC) report, "Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation." The report cites a statistical increase in the numbers of warm nights and a reduction in the numbers of cold nights for 70 to 75 percent of the world, which they attribute to human causes.
The report goes on to list the ways that man-made climate change will impact temperatures, cyclones, drought, wind, waves and precipitation, but not all experts in the field agree with these results.
Dr. Chris Landea, a leading hurricane expert and science and operations officer for the National Hurricane Center, disagrees that any contribution by human action will have an impact of hurricanes. Following Hurricane Katrina, Dr. Landsea resigned from the IPCC over claims stating otherwise.
"All previous and current research in the area of hurricane variability has shown no reliable, long-term trend up in the frequency or intensity of tropical cyclones, either in the Atlantic or any other basin... The evidence is quite strong and supported by the most recent credible studies that any impact in the future from global warming upon hurricanes will likely be quite small," he wrote.
Scientists on both sides of the climate change debate disagree on what long-term trends and history records tell us about the human impact on the environment and our ability to change the climate. One thing they do all agree on, however, is that individual events cannot be considered on their own as evidence for global warming.