Climate Change and Extreme Weather:A New Normal?

Anthony J. BroccoliDirector, Climate and Environmental Change Initiative

Department of Environmental SciencesRutgers University

“Rebuilding a Resilient New Jersey Shore”Monmouth University

December 7, 2012

Mantoloking Ortley Beach

“Extreme weather is the new normal. In the past two years, we have had two storms, each with the odds of a 100-year occurrence.”

- Governor Andrew Cuomo

“Our climate is changing. And while the increase in extreme weather we have experienced in New York City and around the world may or may not be the result of it, the risk that it might be — given this week’s devastation — should compel all elected leaders to take immediate action.”

- Mayor Michael Bloomberg

Four Questions

• What do we mean by “normal” climate?

• Is there a new normal?

• If there is a new normal, were Sandy and other recent extremes harbingers of future events?

• How can we prepare for future weather and climate impacts?

What do we mean by “normal” climate?

• We use the term “normal” to describe the expected range of conditions, including averages and extremes, at a location.

• This definition of normal arises from the concept of stationarity.

• “Stationarity is the assumption that the future will be similar to the past, in a statistical sense.” (Milly 2007, Ground Water News and Views)

• In a stationary climate, the weather events that occur would be drawn from an underlying probability density function with properties that could be determined from the observational record (for example, a “100-year storm”).

Is there a new normal?

Climate Change 101: The Basics

• Combustion of fossil fuels (coal, petroleum, natural gas) emits carbon dioxide into the atmosphere (currently about 9 billion tons of carbon per year).

• Slightly less than half of the carbon dioxide remains in the atmosphere; most of the remainder goes into the ocean (causing ocean acidification).

• Increasing carbon dioxide heats the earth; global temperatures have risen by 1-1.5°F during the past century.

• Increasing temperatures also cause other changes in climate and sea level.

Climate change alters the probability of extreme events

Probability of summer temperature over all Northern Hemisphere land grid boxes (using 1951-1980 baseline)

[Hansen et al. 2012, PNAS]

New Jersey summer temperature trends

[Source: National Climatic Data Center]

Were Sandy and other recent extremes harbingers of future events?

“Boxing DaySnowstorm”

Irene

New Brunswick, NJ

Manville, NJ

Millstone, NJ

Paterson, NJ

October 2011 Snowstorm

Hurricane/Superstorm Sandy

Sandy All previous tropical cyclones passingwithin 50 miles of Atlantic City

Storm surge at The Battery

What the science tells us…

• We do not know if tropical cyclone activity (i.e., intensity, frequency, duration) has changed systematically in the past. In the future, tropical cyclones will probably increase in strength but their number will either decrease or remain essentially unchanged.

• We do not know if severe thunderstorms and tornadoes have become more frequent (because observational methods have improved) and future trends are uncertain.

• Many areas have experienced upward trends in the number of heavy precipitation events and it is likely that such trends will continue throughout the 21st century.

• Record high temperatures and heat waves have been occurring more frequently and they are expected to increase further during the 21st century.

• The ongoing rise in sea level has raised the baseline for coastal flooding from storm surge and the rate of sea level rise will likely accelerate during the remainder of the 21st century.

Sea level trends along NJ coast

16 inches in 100 years

Projection for 2050: 11-25 inches (best estimate of 16”)Projection for 2100: 27-67 inches (best estimate of 43”)

[Source: R. Kopp and K. Miller, Rutgers University, paper in prep.]

Historic water levels at Sandy Hook• >13.2 FT — October 29, 2012 (Sandy)• 10.1 FT — September 12, 1960 (Hurricane Donna) / December 11, 1992. • 9.8 FT — August 28, 2011 (Hurricane Irene). • 9.7 FT — November 7, 1953. • 9.4 FT — September 14, 1944 (Hurricane) / March 6, 1962. • 9.0 FT — November 25, 1950. • 8.9 FT — January 23, 1966. • 8.8 FT — November 12, 1968.• 8.7 FT — MAJOR TIDAL FLOODING BEGINS. • March 29, 1984 / March 13, 1993. • 8.6 FT — September 27, 1985 (Hurricane Gloria) / January 2, 1987 / October 31, 1991. • 8.5 FT — April 13, 1961. • 8.3 FT — February 19, 1972 / March 19, 1996 / March 13, 2010. • 8.2 FT — October 18, 2009. • 8.1 FT — January 31, 2006 / April 16, 2007. • 8.0 FT — October 14, 1955 / December 26, 1969 / December 2, 1974 / April 16, 2011. • 7.9 FT — August 31, 1954 (Hurricane Carol) / December 22, 1972 / October 25, 1980 / February 24, 1998 /

December 25, 2002 / November 14, 2009. • 7.8 FT — October 14, 1977 / November 8, 1977 / March 3, 1994 / December 20, 1995 / January 29, 1998 /

March 30, 2010. • 7.7 FT — MODERATE TIDAL FLOODING BEGINS. • March 20, 1958 / October 22, 1961 / November 10, 1962 / December 25, 1978 / December 3, 1986 / January

4, 1994 / December 13, 1996 / November 14, 1997 / January 3, 2003 / January 3, 2006 / February 12, 2006 / October 7, 2006 / May 12, 2008 / December 12, 2008 / May 17, 2011.

• 6.7 FT — MINOR TIDAL FLOODING BEGINS

The future will not be the same as the past

• “We never had floods like this before. We made preparations but it didn’t do any good…”

• “There was no reason for us to think that the kind of flooding that we actually experienced would happen there.”

• “We had flooding in areas we never had flooding before.”

• “...we've never had flooding before…The house has been in the family since it was built in 1964 and there's never been a problem with weather...ever.”

• “They thought they'd be safe because they'd never had flooding before.”

How can we prepare for future weather and climate impacts?

• Recognize that the past is not an adequate guide to what will happen in the future (finite sample size, changing climate).

• Use information from climate model projections, with careful interpretation, to develop an understanding of the effects of a changing climate baseline.

• Focus on aspects of climate change that we understand with high confidence (such as sea level rise) rather than those that are more uncertain (such as changes in storm frequency/intensity).

• Develop improved methods for making projections of the effects of climate change on high impact weather events.

Example: Estimating future flood return levels

Black curve is for present climate; red and blue curves depict estimated flood return levels for period 2081-2100 under IPCC A1B emissions scenario. (Lin et al. 2012)

Example: Projecting changes in severe weather

Convective available potential energy and specific humidity increase

Vertical wind shear decreases

Net result: Increase in severe thunderstorm environment days

Source: Trapp et al. (2007, PNAS)

Severe thunderstorms and tornadoes occur where moisture is abundant , the atmosphere is unstable, and vertical wind shear is large.

Four Questions

• What do we mean by “normal” climate?Implicit assumption: Climate is quasi-stationary

• Is there a new normal?Stationarity is dead.

• If there is a new normal, were Sandy and other recent extremes harbingers of future events?Yes for some types of extremes; uncertain for others.

• How can we prepare for future weather and climate impacts?Use best available science.