A panel of distinguished University of Arizona climate experts spoke before a crowd of about 100 in the Kiva auditorium in the Student Union Memorial Center, commenting on the latest United Nations report on climate change
, published just a few hours prior. The panel interpreted the report's findings and shared implications for the Southwest.
While the latest report largely reads as a continuation of the previous one issued in 2007, according to the UA panelists, the group pointed out that significant advances in science and modeling capabilities have resulted in data of a much better quality and fraught with less uncertainties.
, a professor in the UA's Department of Geosciences
who studies corals and other climate records for clues about past climate, opened the presentation with a brief overview of the report's core conclusions and projections for the current century.
"Here in Arizona, we are in the bull's-eye of climate change," Cole said. "We are warming faster than almost anywhere else, we are drying out because of this warming, we have a rapid rate of population growth, we are experiencing extreme climate events and hotter and drier conditions. Climate change is happening, right here and right now."
Wet gets wetter, dry gets drier
"It's going to be a 'wet-gets-wetter, dry-gets-drier' kind of world," she explained. "The desert regions are going to be more arid, while the equatorial and higher latitudes are going to see even more moisture."
"The warmer we make the world, the stronger the patterns we are going to see," Cole said, cautioning that, "warming does not occur uniformly, so your location doesn't tell you much about global warming."
In the course of global temperature rising, Cole said the report suggests a complete loss of sea ice in the Arctic during the summer months by about 2050.
"This is tremendously impactful," she said, "not just for life in the polar regions and marine life in general, but geopolitically as well."
Russia, the U.S. and other nations are interested in the resources that might become more accessible once the ice cover is gone, including access to oil, ocean floor mining, fishing shipping.
One of the greatest threats to marine organisms – and with them, entire food webs – is ocean acidification, brought about by increased emissions of carbon dioxide, or CO2, into the atmosphere. CO2 makes ocean water more acidic, making it more difficult for organisms, such as certain phytoplankton, corals and other invertebrates, to make hard shells.
Ocean acidity is much worse than expected, Cole said, adding that worldwide, the seawater has changed from the pre-industrial baseline enough to impact shell-building organisms already.
The new report predicts a global rise in sea level of 0.5 to 1 meter or about two to three-and-a-half feet by the end of the century.
"We are still in the early days of understanding sea level rise," Cole said, as scientists struggle to accurately represent the contributions of melting glaciers around the world and melting ice sheets in Greenland and Antarctica into their simulation models. "However, all models indicate sea level is rising faster and faster," and it is important to note that entities like the National Oceanic and Atmospheric Administration and the Department of Defense are using numbers up to 2 meters for their planning efforts to deal with higher sea levels.
Cole reminded the audience that because this is a consensus report among thousands of scientists, it is a fairly conservative document.
"The IPCC has never issued statements that turned out to be wildly radical in terms of climate change," Cole said.
Heat may come back to haunt us
One of the less expected findings of the latest climate assessment is that the deep oceans trap and store large amounts of heat, as Joellen Russell
, an associate professor in the UA's Department of Geosciences, pointed out.
"It turns out the deep ocean is taking up 93 percent of the heat in Earth's atmosphere," Russell said. "When it's getting hot here in Arizona, what you feel is that tiny bit of heat that doesn't make it into the ocean."
Russell said while many scientists used to believe that only the upper 700 meters of the oceans are getting warmer, it has become clear that the heat content is rising at all depths, down to the deepest reaches of the oceans.
"Our oceans are doing some very heavy lifting for us," Russell said. "As the Earth is warming, they store a lot of that heat. Right now, we see a bit of a slowdown in the rise of global temperature because it's taken up by the deep ocean, but that heat is not going away. With natural variation, we should expect that heat to come back and haunt us at some point."
Carbon dioxide: Uncharted territory
According to Monson, the concentration of carbon dioxide, a greenhouse gas trapping heat in the Earth's atmosphere, continues to rise.
"The observed CO2 concentration in the atmosphere falls right in line with the projections all the way back to the first climate assessment report," he said. "Earlier this year, it reached 400 parts per million, higher than it has ever been in the last 800,000 years, which spans almost the entire human existence. In terms of CO2 concentration, we really are in uncharted territory."
Monson explained that weakening of plants by temperature and drought stress and limitation of nutrients will likely offset the capacity of forests to scrub CO2 from the atmosphere.
Monson also said the new report emphasized in even stronger language the increasing role of nitrous oxide as a greenhouse gas, mostly from increased fertilizer use. In addition, aerosols, tiny particles that remain suspended in the atmosphere and are believed to dampen the Earth's warming by reflecting heat back into space, have exhibited decreased atmospheric concentrations, mostly due to the cleaning of pollutant emissions, such as those of sulfate, from coal-fired power plants.
"It turns out aerosols that we have relied upon as working against global warming are becoming increasingly less abundant because they have other detrimental effects on the environment, such as promoting acidic rain; this has created even more potential for greenhouses such as carbon dioxide, methane and nitrous oxide to warm the planet," Monson said.
"The main message is that we keep analyzing these instrumental records and they keep looking the same. This helps address concerns by skeptics who have questioned whether the data are good."
"For Arizona, we find that we have the strongest temperature trend of the lower 48 states, and we have known that, but the new report is confirming that.
The outlook for the Southwest
Cole wrapped up the panel by presenting an outlook for the Southwest.
"We will see more of the hot and dry pre-monsoon season, the season most people here find the least bearable. We'll see a tendency for decrease in summer rainfall, but at the same time, those rains are going to come in more intense storms. There will be longer dry spells during the monsoon season."
Referencing a recent study not related to the report, Cole said that warming alone could reduce the Colorado river flow by up to 35 percent, without taking into account changes in precipitation.
The panel concluded by saying that while projections look grim, there is reason to be optimistic.
"Nobody is asleep at the wheel," Crimmins said. "I don't want to sugarcoat it, this is not to say we don't have challenges, but I don't think we'll wake up tomorrow and there's no water. The UA has made a lot of efforts to produce the science and plug it into the management efforts."
"One of the triumphs of this assessment is that in none of the previous, we were able to track carbon cycling through the Earth system," Russell explained. "Now we have these new capabilities to include those new models. They are extraordinary and they take into account ocean acidification, carbon nutrient cycling and processes we could simply not get to before."
Monson said, "I'm optimistic about climate science; it's a vibrant field, it is not being politicized, we have more computing power, and at least humanity is doing a better job at understanding this."
Cole agreed. "I'm optimistic, too. I'm really proud of the way the UA is fostering this kind of climate work. We see fantastic graduate students coming in here who bring fresh perspectives and innovative ideas to the table. It is encouraging to see climate change being picked up as a real risk management issue outside the scientific community. We have tackled environmental problems in the past and we can do it again."