Global Warming and Large Scale Climate Phenomena

Hurricane Isabel, seen from the International Space Station. NASA

The weather we experience is a manifestation of the climate we live in. Our climate is affected by global warming, which has led to many observed changes, including warmer sea temperatures, warmer air temperatures, and changes in the hydrological cycle. In addition, our weather is also affected by natural climate phenomena that operate over hundreds or thousands of miles. These events are often cyclic, as they reoccur at time intervals of various lengths. Global warming can affect the intensity and return intervals of these events large-scale. The Intergovernmental Panel on Climate Change (IPCC) has recently issued its 5th Assessment Report, with a chapter devoted to the effects of climate change on these large scale climate phenomena. Here are some important findings:

  • Monsoons are seasonal wind reversal patterns accompanied with significant rainfall. They are responsible, for example, for the summer thunderstorm periods in Arizona and New Mexico, and the torrential downpours in India’s rainy season. Overall, monsoon patterns will increase in area and intensity with continued climate change. They will start earlier in the year and end later than what had been the average.
  • In North America, where monsoons are limited to the U.S. Southwest region, no change in precipitation due to global warming has been clearly observed. A decrease in the length of the season has been observed, though, and monsoons are expected to be delayed during the year. So there appear to be no relief in sight for the observed (and predicted) increase in frequency of extreme summer temperatures in the U.S. Southwest, contributing to drought.
  • The amount of precipitation from monsoon rains is forecasted to be higher in the more pessimistic scenarios considered by the IPCC. In a scenario of continued reliance on fossil fuel and the absence of carbon capture and storage, total precipitation from monsoons, globally, is estimated to increase by 16% by the end of the 21st century.
  • The El Niño Southern Oscillation (ENSO) is a large area of unusually warm water that develops in the Pacific Ocean off South America, affecting weather over a large portion of the globe. Our ability to model future climates while taking into account El Niño has improved, and it appears that variability in precipitation will increase. In other words, some El Niño events will produce more rainfall and snowfall than expected in some areas of the globe, while others will produce less precipitation than expected.
  • The frequency of tropical cyclones (tropical storms, hurricanes, and typhoons) is likely to stay the same or decrease, globally. The intensity of these storms, both in wind speed and precipitation, is likely to increase. There are no clear changes predicted for the track and intensity of North American extra-tropical storms (Hurricane Sandy became one of those cyclonic storms outside of the tropics).   

Predictive models have improved significantly in the last few years, and they are currently being refined to resolve remaining uncertainties. For example, scientists have little confidence when trying to predict changes in monsoons in North America. Pinpointing, or downscaling the effects of the El Niño cycles or the intensity of tropical cyclones in specific areas has also been difficult. Finally, the phenomena described above a largely know by the public, but there are many other cycles: examples include the Pacific Decadal Oscillation, the Madden-Julian Oscillation, and the North Atlantic Oscillation. The interactions between these phenomena, regional climates, and global warming make the business of scaling down global change predictions to specific locations bewilderingly complex.