September 19, 2013

Is Bjørn Lomborg [“Going to extremes over climate change,” Sunday Opinion, Sept. 15] unaware of a recent report by the National Oceanic and Atmospheric Administration, “Explaining Extreme Events of 2012 from a Climate Perspective,” which has been getting a lot of press, including in The Post [“How much are we changing the climate?,” Health and Science, Sept. 10]? The NOAA report looked at 12 recent extreme-weather events around the world and found that climate change was influential in six of them. These include floods, storms, heat waves and declining Arctic sea ice levels. The basic connection between global warming and extreme weather has been clearly established. With more global warming, higher temperatures evaporate more moisture off the oceans into the air. Warmer air can hold more water vapor, leading to stronger rains. At the same time, worse droughts are a result of extra heat evaporating more water out of the soil.

Global warming may not be the cause of each and every weather event, but it can cause those events to be more damaging. And as the temperature keeps rising, get ready for more of them.

Bill Brockhouse, Alexandria

The writer is a climate leader for the Climate Reality Project.

Bjørn Lomborg was correct when he quoted the recent Nature paper that I co-wrote as saying that, when averaged across the world, the size of year-to-year temperature fluctuations has been remarkably invariant over the past five decades. But this apparent conservation property of the climate system hides key regional differences. Temperature volatility has decreased markedly for much of the tropics, but this is balanced by major increases over large parts of Europe and the United States. This is all in addition to a general warming that is occurring everywhere. Society should still take seriously the risks associated with changing patterns of extreme-weather events, some of which might be due to a buildup of atmospheric greenhouse gas concentrations.

Chris Huntingford, Wallingford, England

The writer is climate modeler for the UK Centre for Ecology and Hydrology.

Bjørn Lomborg claimed that high nighttime temperatures make temperature differences “less extreme,” as if that’s a good thing. But high night temperatures kill because they translate into no cooling respite for the young, old and the sick, those who are at the most risk during deadly heat waves. In addition, some food crops need cool nights to grow; their yields will decrease as nights warm up.

Mr. Lomborg also claimed that more intense precipitation will reduce water scarcity without noting the increased risk of loss of lives and property from the flooding that generally accompanies such events. The current situation around Boulder, Colo., reminds us just how disruptive rainstorms can be.

Likewise, hurricanes in the Atlantic are expected to shift to higher intensity. In the meantime, rising seas are already raising flood levels and adding to the loss of property, as we saw in Superstorm Sandy. Sea level rise added to the devastation by combining with storm surge; as a result, in New York City alone, where sea level is about a foot higher than a century ago, an additional 45,000 people were affected.

The science is always being perfected, but the warning is clear: Climate change is already to blame for some extreme weather, and these extremes and others are expected to intensify with further warming.

Michael Oppenheimer, New York

The writer, a professor of geosciences and international affairs at Princeton University, is a co-author of U.N Intergovernmental Panel on Climate Change reports.