NPCC

New York City Panel on Climate Change

NPCC4: Tail risk, climate drivers of extreme heat, and new methods for extreme event projections

Introduction

Climate Science Work Group Co-Chairs: Christian Braneon and Luis Ortiz

Anthropogenic climate change is fundamentally linked to the rapid increase in greenhouse gas (GHG) emissions propelled by the Industrial Revolution and the European colonial systems that enabled it.

This NPCC4 chapter provides the latest assessment of the drivers and impacts of climate projections in New York City. It builds on earlier assessments and describes new methods to develop predictions of sea level rise, temperature change, and precipitation for the city. The chapter also presents updated “projections of record” for sea level rise, air temperature changes, extreme heat, precipitation, compound risks and extreme events to inform the City’s ongoing policy efforts.

NPCC4’s focus on equity highlights that vulnerability to climate hazards and stressors is inequitably distributed in NYC. In response, this chapter emphasizes the equity implications of climate change adaptation.

from the IPCC 5th Assessment

The data show average annual air temperatures have increased over the last 70 years across the city. In addition, the daily nighttime temperature is increasing at a faster rate than daytime temperatures. The total number of hot days and nights is expected to increase, as is the frequency of heat waves. Total annual rainfall is also predicted to increase, though with less certainty than air temperature predictions, along with the number of extreme rainfall events. Sea level is also predicted to rise and potentially accelerate as the century progresses.

In addition to offering these projections, the chapter also describes how large-scale climate processes, along with local land and infrastructure characteristics, affect extreme heat in the city.  Local drivers in New York City include urban infrastructure (e.g., streets, sidewalks, and buildings) and the natural environment (e.g., shrubs, trees, and grasses). Local and physical factors can lead to inequitable exposure to risks from extreme heat, including stronger urban heat islands. Considering different experiences of extreme heat across the city is important for developing an equitable strategy.

Lastly, the chapter discusses the implications of low probability extreme weather and climate change scenarios, known as “tail risks.” These tail risks can have significant consequences for cities (e.g., Hurricane Sandy), so it is important to consider their implications. The chapter discusses tail risks associated with rainfall, sea level rise, and tropical cyclones.

Photo Credit: University Neighborhood Housing Program Cool Roofs: Dana Ullman, UNHP, City of New York Mayor’s Office of Climate and Environmental Justice

Read the Chapter

Authors

Luiz Ortiz, Ph.D. Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, Fairfax, VA

Christian Braneon, Ph.D. CUNY Institute for Demographic Research, City University of New York, New York, NY, NASA Goddard Institute for Space Studies, New York, NY., Columbia Climate School, Columbia University, New York, NY

Radley Horton, Ph.D. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, Columbia Climate School, Columbia University, New York, NY

Dan Bader, MA Center for Climate Systems Research, Columbia University, New York, NY, NASA Goodard Institute for Space Studies, New York, NY

Philip Orton, Ph.D. Stevens Institute of Technology, Hoboken, NJ

Vivien Gornitz, Ph.D. NASA Goodard Institute for Space Studies, New York, NY

Bernice Rosenzweig, Ph.D. Department of Environmental Science, Sarah Lawrence College, Bronxville, NY

Timon McPhearson, Ph.D. Urban Systems Lab, The New School, New York, NY, Cary Institute of Ecosystem Studies, Millbrook, NY, Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden

Lauren Smalls-Mantey, Ph.D. New York City Department of Health and Mental Hygiene, New York, NY

Hadia Sheerazi, dual MSc. Rocky Mountain Institute, New York, NY

Franco Montalto, Ph.D. Department of Civil, Architectural and Environmental Engineering, Drexel University, Philadelphia, PA

Mobin Rahimi-Golkhandan, MSc. Department of Civil, Architectural and Environmental Engineering, Drexel University, Philadelphia, PA

Colin Evans, Ph.D. Earth and Atmospheric Sciences, Cornell University

Art DeGaetano, Ph.D.  Earth and Atmospheric Sciences, Cornell University

Evan Mallen, Ph.D. Urban Climate Lab, School of City and Regional Planning, Georgia Institute of Technology, Atlanta, GA

LaTonya Carter, MSc. Department of Geography and Geoinformation Science, George Mason University, Fairfax County, VA

Kathryn McConnell, Ph.D. Population Studies and Training Center, Brown University, Providence, Rhode Island

Talea Mayo, Ph.D. Department of Mathematics, Emory University, Atlanta, GA

Maya Buchanan, Ph.D. WSP USA, Portland, OR

Summary

Related Links

  • Key Message 1

    NPCC4 analysis of the impact of hot models on the CMIP6 ensemble found no statistically significant difference between the temperature and precipitation projections of record and alternative projections that do not include models with equilibrium climate sensitivity outside the expected range.

    The CMIP6 climate model ensemble used to create the temperature and precipitation projections of record contains three models that display higher-than-expected sensitivity of temperatures to greenhouse gases. These so-called “hot models” lead to higher global mean temperatures. However, the impact of high climate sensitivity appears small with our approach to developing local projections for NYC. Nevertheless, more research is needed to better understand (1) the impact of the high climate sensitivity on the representation of key large scale climate processes, (2) the model physics leading to high sensitivity in the first place, and (3) the constraints on the planet’s equilibrium climate sensitivity.

  • Key Message 2

    The high tail end of sea level rise will be governed by the future stability of the ice sheets, and in particular, that of the West Antarctic Ice Sheet (WAIS), with ~3 m of SLR potential if all its marine-based ice melted, and also that of the Greenland Ice Sheet (~7 m SLR equivalent).

    Troubling signs of ice shelf thinning and ocean warming around WAIS and an approaching temperature tipping point over Greenland raise the possibility of faster and higher sea level rise than projected by most climate models, increasing the risks associated with coastal flooding. Additional research is needed to gain a better understanding of all the processes governing ice sheet behavior with rising temperatures. Stakeholders concerned with long-term planning need to examine plausible scenarios at the extreme upper tail of the sea level rise distribution.

  • Key Message 3

    While occurrence of extreme heat events in NYC is governed in great part by climatic events taking place at large spatial scales, local urbanization patterns play a key role in the spatial distribution of temperatures within the city.

    These local patterns, which include a range of factors like distribution of green spaces and urban geometry, play the most significant role in the generation of physical process that lead to the urban heat island (UHI). Moreover, extreme heat events exacerbate this intra-urban excess temperatures, increasing exposure to deadly heat of populations without access to adaptive measures and cooling infrastructure (e.g., cooling centers, tree shade). Future work is needed to assess the impact of a warming climate on intra-urban heat variability in order quantify the effect of climate change on spatial inequities of heat exposure.