Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming is highly dangerous

James Hansen¹, M. Sato1, P. Hearty², R. Ruedy^3,4, M. Kelley^3,4, V. Masson-Delmotte⁵, G. Russell⁴, G. Tselioudis⁴, J. Cao⁶, E. Rignot^7,8, I. Velicogna^8,7, E. Kandiano⁹, K. von Schuckmann¹⁰, P. Kharecha1,⁴, A. N. Legrande⁴, M. Bauer11, and K.-W. Lo<sup>3,4

1</sup>Climate Science, Awareness and Solutions, Columbia University Earth Institute, New York, NY 10115, USA
²Department of Environmental Studies, University of North Carolina at Wilmington,
North Carolina 28403, USA
³Trinnovium LLC, New York, NY 10025, USA
⁴NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
⁵Institut Pierre Simon Laplace, Laboratoire des Sciences du Climat et de l’Environnement (CEA-CNRS-UVSQ), Gif-sur-Yvette, France
⁶Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China
⁷Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109, USA
⁸Department of Earth System Science, University of California, Irvine, California, 92697, USA
⁹GEOMAR, Helmholtz Centre for Ocean Research, Wischhofstrasse 1–3,
Kiel 24148, Germany
¹⁰Mediterranean Institute of Oceanography, University of Toulon, La Garde, France
¹¹Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA

Abstract

There is evidence of ice melt, sea level rise to +5–9 m, and extreme storms in the prior interglacial period that was less than 1◦C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disin- tegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Dou- bling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 10 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge.

Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean tem- perature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic as well as the Southern Ocean, increases tropospheric horizontal temperature gradi- ents, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean’s role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate.

The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10–40 year range.

We conclude that 2 ◦C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth’s energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.

1. Introduction

Humanity is rapidly extracting and burning fossil fuels without full understanding of the consequences. Current assessments place emphasis on practical effects such as increasing extremes of heat waves, droughts, heavy rainfall, floods, and encroaching seas (IPCC, 2014; USNCA, 2014). These assessments and our recent study (Hansen et al., 2013a) conclude that there is an urgency to slow carbon dioxide (CO2) emis- sions, because the longevity of the carbon in the climate system (Archer, 2005) and persistence of the induced warming (Solomon et al., 2010) may lock in unavoidable highly undesirable consequences.

Despite these warnings, global CO2 emissions continue to increase as fossil fuels remain the primary energy source. The argument is made that it is economically and morally responsible to continue fossil fuel use for the sake of raising living standards, with expectation that humanity can adapt to climate change and find ways to minimize effects via advanced technologies.

We suggest that this viewpoint fails to appreciate the nature of the threat posed by ice sheet instability and sea level rise. If the ocean continues to accumulate heat and increase melting of marine-terminating ice shelves of Antarctica and Greenland, a point will be reached at which it is impossible to avoid large scale ice sheet disintegration with sea level rise of at least several meters. The economic and social cost of losing functionality of all coastal cities is practically incalculable. We suggest that a strate- gic approach relying on adaptation to such consequences is unacceptable to most of humanity, so it is important to understand this threat as soon as possible.

The full report is available at this link → http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015.pdf

Auto fuel efficiency bill signed into law

by Janet Ritz
Martin Muse

A bill raising auto fuel standards for the first time in over thirty years was signed by President Bush today, requiring that automobiles average 35 miles per gallon by 2020 and raising federal support for alternative fuel and conservation programs.

It passed by a wide margin in the House, but was stalled momentarily in the Senate when Republicans filibustered out a provision that would have eliminated tax breaks for oil companies and required utility companies to provide a portion of their power from alternative sources.

After which, the head of the Sierra Club referred to the bill as a partial victory and vowed to put through the redacted provisions at a later date.

One area of the bill that has been praised is the instruction to use non-food sources for biofuels (i.e. switch grass and wood chips instead of corn). The other is the raising of the fuel standard itself, which should help to reduce the amount of greenhouse gases currently emitted.

More information here.

Everything but the Oceans' Sinks

by The Environmentalist Staff

Amidst alarms raised about the loss of ice in the polar regions, the extreme droughts and floods across the US, the floods in the UK earlier last year, the increasingly unstable nature of the weather worldwide, a new concern has been raised about the Southern Oceans' inability to absorb and store CO2:

The Southern Ocean around Antarctica is so loaded with carbon dioxide that it can barely absorb any more, so more of the gas will stay in the atmosphere to warm up the planet, scientists reported on Thursday.

Human activity is the main culprit, said researcher Corinne Le Quere, who called the finding very alarming. The phenomenon wasn't expected to be apparent for decades, Le Quere said in a telephone interview from the University of East Anglia in Britain. "We thought we would be able to detect these only the second half of this century, say 2050 or so," she said. But data from 1981 through 2004 show the sink is already full of carbon dioxide.

This is very alarming. The southern ocean is the the world's strongest carbon sink, a "reservoir that absorbs and stores more carbon than they release, thereby offsetting greenhouse gas emissions." If the sink has been filled, as seems to be the case, that carbon has no where to go but to the atmosphere, as our other sinks: the forests, the land, the rest of the oceans, are all stressed by loss of habitat, increased warming and their own carbon levels. Which means a speed-up of warming at a far faster rate than had been previously predicted.

This increase in the Southern Ocean has been attributed to a change in wind patterns caused by the following climate forcings:

1. Ozone depletion. The reduction of ozone has changed the temperature and increased wind patterns in the Southern Hemisphere. As these winds flow across the oceans they pull natural CO2 to the surface. This is a problem because natural CO2 does not bind easily with human caused carbon. The balance had been maintained through past wind patterns, which had helped to combin the two types of carbon. With the increased winds and level of stored carbon, that natural mixture has been disrupted...
   

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