Climate researcher Kevin Trenberth is troubled by time, both on the short and longer scale. On the short scale, measurements taken since the beginning of the millennium suggest that the Earth should have heated up more than it already has. Yet because we only have a few years of these measurements, we have never seen this “missing heat” situation happen before, and have no explanation for it.
On the longer scale, Trenberth notes that it takes decades for the full impact of any increase in the Earth’s temperature to emerge, and this is one of the key problems of climate change. “The actions we take now mainly have effects 50 years from now and beyond,” he tells Simple Climate. “Carbon dioxide has a long lifetime and so does the infrastructure that produces it. The oceans and climate system respond slowly.”
Trenberth is head of the Climate Analysis Section at the US National Center for Atmospheric Research in Boulder, Colorado. Last week, writing in the journal Science, he highlighted a gap between satellite measurements of the balance of energy the Earth has absorbed from the Sun and recent temperature changes. He notes that more energy has been absorbed than released back into space for some time, but since 2005 it has not led to the temperature rises expected. Humans haven’t been looking at radiation absorbed and emitted from the Earth for long enough to have seen this before, Trenberth explains. “The record is short,” he says. “Radiation measurements began in 2000 and prior to then we just have a 4 year period from 1985 to 1989.”
The additional heat may be stored somewhere that it hasn’t been measured, Trenberth suggests, where it is poised to reappear and affect the climate. A prime candidate location is deep in the ocean. “A moderate El Niño has developed since June 2009, making ocean temperatures a lot higher,” he points out. El Niño is the warm phase of a weather pattern that occurs on average every five years. Therefore it has emerged before when there was no missing energy, so without further data it is currently too early to say whether it will explain the gap.
The amount of energy flowing into the Earth and back out into space in a given period is far greater than all of humanity’s power generation, Trenberth points out. However, the CO2 produced by burning fossil fuels to produce our energy has a disproportionate impact. “Humans affect the climate by modifying natural energy flows, through changing atmospheric composition and changing the greenhouse effect,” he says. “The energy we burn in electric power generation is about 1/9000th of the natural flow, and the change in greenhouse effect is about 100 times greater: about a 1% effect.”
Thanks to the 50 year time lag, we are yet to see the full effects of fossil fuel consumption through the 20th Century. “Carbon dioxide has gone up over 35% since pre-industrial times and over half of that is since 1970,” Trenberth explains. “This changes the greenhouse effect and traps radiation that would otherwise escape to space, producing warming. The warming is manifested in many ways, not just increasing surface temperatures, but also melting ice, and changing rainfall. Since 1970 the effects are large enough to be outside the bounds of natural variability.”
Trenberth does note, though, that natural variability means that even with the effects of global warming temperatures are unlikely to rise every single year. So, instead of using how warm we each individually feel to follow climate change we should be looking at rising sea levels, warmer oceans and overall temperatures on the surface of the planet. We can also look at decreasing Arctic sea ice and melting glaciers in Greenland, as well as increasing extremes of heavy rain and snow and droughts. “All of these are well established and global warming is unequivocally happening,” he says.