AGU journal highlights -- Aug. 12, 2008

1. Fast rise of scorching days predicted

Assessing and predicting the frequency and strength of extreme climate events are critical to determining the consequences of future climate change. Motivated by western Europe's exceptionally hot summers of 2003 and 2006, Sterl et al. use an ensemble of climate models to investigate changes in extreme values of climate variables. Using a statistical method for determining return intervals for extreme events, the authors find that the recurrence time for extremely high temperatures will not only increase as average temperatures rise, but will also increase at a faster rate than rising average temperatures. After correcting for model biases, the authors also find that by the end of this century, extreme temperatures will far exceed 40 degrees Celsius (104 degrees Fahrenheit) in southern Europe and the U.S. Midwest and will even reach 50 degrees C (122 degrees F) in northeastern India and most of Australia. Because any point on land within roughly 40 degrees of the equator will have a 10 percent chance of exceeding 48 degrees C (118 degrees F) every decade by the end of this century, the authors urge that the risk to populations be taken very seriously.

Title:
When can we expect extremely high surface temperatures?

Authors:
Andreas Sterl, Camiel Severijns, Wilco Hazeleger, Geert Jan van Oldenborgh, Gerrit Burgers, and Peter van Velthoven: Royal Netherlands Meteorological Institute, De Bilt, Netherlands;
Henk Dijkstra, Michiel van den Broeke, and Peter Jan van Leeuwen: Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands;
Bart van den Hurk: Royal Netherlands Meteorological Institute, De Bilt, Netherlands; also at Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2008GL034071, 2008; http://dx.doi.org/10.1029/2008GL034071

2. Northeast U.S. lake yields 1000-year hurricane record

Recent studies suggest that hurricane activity may be increasing due to human-induced global warming. However, assessing recent trends in the context of natural hurricane variability is difficult because instrumental records extend back only about 130 years. Noting that natural archives such as lake sediments can preserve storm history, Besonen et al. examine a sediment record from the Lower Mystic Lake (near Boston, Massachusetts) that contains 1000 years of annual laminations. Some laminations include anomalous graded beds. Within the historical record, 10 out of 11 of the most prominent graded beds correspond to years in which hurricanes struck the Boston area. Assuming that these graded beds represent deposition related to precipitation and wind-driven disturbances from hurricanes, extrapolating back within the sediment record reveals an annually resolved history of category 2?? hurricane occurrence spanning the past 1000 years. This signal, unique to Boston, shows strong centennial-scale variations in hurricane frequency and includes a period of increased activity between the twelfth and sixteenth centuries. Decreased activity occurred during the eleventh as well as the seventeenth through nineteenth centuries.