Examination of the possible effects of global warming on hurricanes

Kevin Trenberth of the Climate Analysis Section (CAS) of the
Climate and Global Dynamics Division (CGD) of NCAR
has been looking at possible effects of global warming on hurricanes.

See Hurricane Pictures

In 'Energy Budgets of Atlantic Hurricanes and Changes from 1970' found in Geochemistry, Geophysics, Geosystems in September 2008, authors Kevin Trenberth and John Fasullo say: 'On the basis of the current observational record of tropical cyclones and sea surface temperatures (SSTs) in the Atlantic, estimates are made of changes in surface sensible and latent heat fluxes and hurricane precipitation from 1970-2006. The best track data set of observed tropical cyclones is used to estimate the frequency that storms of a given strength occur after 1970. Empirical expressions for the surface fluxes and precipitation are based on simulations of Hurricane Katrina in August 2005 with the advanced Weather and Research Forecasting (WRF) model at 4 km resolution without parameterized convection.'

Read the full article: Energy Budgets of Atlantic Hurricanes and Changes from 1970

In 'Water and Energy Budgets of Hurricanes: Case Studies of Ivan and Katrina' found in Journal of Geophysical Research in December 2007, authors, which include Kevin Trenberth and John Fasullo, say: "Overall, the hurricane expands in size as sea surface temperatures (SSTs) increase, the environmental atmospheric moisture increases at close to the Clausius-Clapeyron equation values of about 6% K-1 and the surface moisture flux also increases mainly from Clausius-Clapeyron effects and the changes in intensity of the storm. The environmental changes related to human influences on climate since 1970 have increased SSTs and water vapor, and the results suggest how this may have altered hurricanes and increased associated storm rainfalls, with the latter quantified to date to be of order 6 to 8%."

Read the full article: Water and Energy Budgets of Hurricanes: Case Studies of Ivan and Katrina

In 'Water and Energy Budgets of Hurricanes and Implications for Climate Change' found in Journal of Geophysical Research in December 2007, authors Kevin Trenberth and John Fasullo say: "What role, if any, do hurricanes and tropical cyclones have in our climate system? Why do hurricanes exist? These rather fundamental questions are the motivation for the research outlined here and have substantial implications for both our understanding and modeling of the climate system and its variability."

Read the full article: Water and Energy Budgets of Hurricanes and Implications for Climate Change

In 'Hurricane and Global Warming - Potential Linkages and Consequences' found in Bulletin of the American Meteorological Society in May 2006, authors, which include Kevin Trenberth and Jim Hurrell, say: "The potential relationships between tropical cyclones and global climate change are scientifically and socially complex, with great implications for society. The exceptional nature of the 2005 North Atlantic hurricane season alone provides great incentives for better understanding the full range of interactions and causes and effects thereof."

Read the full article: Hurricane and Global Warming - Potential Linkages and Consequences

In 'Atlantic Hurricanes and Natural Variability in 2005', published in Geophysical Research Letters in June 2006, authors Kevin Trenberth and Dennis Shea say: "The 2005 North Atlantic hurricane season (1 June to 30 November) was the most active on record by several measures, surpassing the very active season of 2004 and causing an unprecedented level of damage. Sea surface temperatures (SSTs) in the tropical North Atlantic (TNA) region critical for hurricanes (10° to 20° N) were at record high levels in the extended summer (June to October) of 2005 at 0.9°C above the 1901-70 normal and were a major reason for the record hurricane season. Changes in TNA SSTs are associated with a pattern of natural variation known as the Atlantic Multi-decadal Oscillation (AMO). However, previous AMP indices are conflated with linear trends and a revised AMO index accounts for between 0 and 0.1°C of the 2005 SST anomaly. About 0.45°C of the SST anomaly is common to global SST and is thus linked to global warming and, based on regression, about 0.2°C stemmed from after-effects of the 2004-2005 El Niño."

Read the full article: Atlantic Hurricanes and Natural Variability in 2005

In 'Uncertainty in Hurricanes and Global Warming' in Science magazine June 2005, Kevin Trenberth says: "During the 2004 hurricane season in the North Atlantic, an unprecedented four hurricanes hit Florida; during the same season in the Pacific, 10 tropical cyclones or typhoons hit Japan (the previous record was six). Some scientists say that this increase is related to global warming; others say that it is not. Can a trend in hurricane activity in the North Atlantic be detected? Can any such trend be attributed to human activity? Are we even asking the right questions?"

Read the full article: Uncertainty in Hurricanes and Global Warming

In October 2004, Kevin Trenberth participated in a news conference 'Hurricanes and Global Warming' at the Center for Health and Global Environment, Harvard Medical School. Kevin's comments included "Let me focus then on the science of climate change and the physical aspects of the climate change that are going on. The first key point, as Jim McCarthy said, is that the atmospheric composition is changing due to human activities. There's a buildup of carbon dioxide; it's around 31, 32% higher than pre-industrial levels. Global warming is happening and there is a lot of evidence for that, as others have already stated, and the global mean temperature is increasing."

Read the entire transcript: Hurricanes and Global Warming News Conference

How much has global warming contributed to recent enhanced hurricane activity?

No, hurricane Katrina was not caused by global warming. But observations and our scientific analysis of them strongly suggests that there is a non-trivial human influence making such storms more intense and damaging.

There is no doubt that climate is changing, and humans are partly responsible. Global mean air temperatures are running 1 degree F or more above pre-1970s values. While 1998 remains the warmest year on record, 2002, 2003 and 2004 follow closely behind. Sea level has gone up over 1ΒΌ inches in the past decade, as the ocean waters warm and expand and glaciers melt. Using climate models, these changes have been definitively linked to increases in greenhouse gases in the atmosphere, most notably carbon dioxide, which has increased 32% in the past century and half of that increase has occurred since 1970. This increase is caused by human activities and especially the burning of fossil fuels.

Read more about it: Global Warming and recent hurricane activity

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