Assessing "Dangerous Climate Change": Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature

This paper, by an international team of scientists, points out the clear and present danger that today's children may be handed a deteriorating climate with consequences out of their control. 

Dr. James Hansen
by James Hansen, Pushker Kharecha, Makiko Sato, Valerie Masson-Delmotte, Frank Ackerman, David J. Beerling, Paul J. Hearty, Ove Hoegh-Guldberg, Shi-Ling Hsu, Camille Parmesan, Johan Rockstrom, Eelco J. Rohling, Jeffrey Sachs, Pete Smith, Konrad Steffen, Lise Van Susteren, Karina von Schuckmann, James C. Zachos

We conclude that the widely accepted target of limiting human-made global climate warming to 2 degrees Celsius (3.6 degrees Fahrenheit) above the preindustrial level is too high and would subject young people, future generations and nature to irreparable harm. Carbon dioxide (CO2) emissions from fossil fuel use must be reduced rapidly to avoid irreversible consequences such as sea level rise large enough to inundate most coastal cities and extermination of many of today's species. Unabated global warming would also worsen climate extremes. In association with summer high pressure systems, warming causes stronger summer heat waves, more intense droughts, and wildfires that burn hotter. Yet because warming causes the atmosphere to hold more water vapor, which is the fuel that drives thunderstorms, tornadoes and tropical storms, it also leads to the possibility of stronger storms as well as heavier rainfall and floods. Observational data reveal that some climate extremes are already increasing in response to warming of several tenths of a degree in recent decades; these extremes would likely be much enhanced with warming of 2°C or more.

We use evidence from Earth's climate history and measurements of Earth's present energy imbalance as our principal tools for inferring climate sensitivity and the safe level of global warming. The inferred warming limit leads to a limit on cumulative fossil fuel emissions.

It is assessed that humanity must aim to keep global temperature close to the range occurring in the past 10,000 years, the Holocene epoch, a time of relatively stable climate and stable sea level during which civilization developed. The world cooled slowly over the last half of the Holocene, but warming of 0.8°C (1.4°F) in the past 100 years has brought global temperature back near the Holocene maximum.

We note that policies should emphasize fossil fuel carbon, not mixing in carbon from forest changes as if it were equivalent. Most of the carbon from fossil fuel burning will stay in the climate system for of order 100,000 years. Of course carbon dioxide from deforestation also causes warming and policies must address that carbon source, but good land use policies could restore most of that carbon to the biosphere on a time scale of decades to centuries. However, maximum biospheric restoration is likely to be only comparable to the past deforestation source, so fossil fuel sources must be strictly limited.

We conclude that human-made warming could be held to about 1°C (1.8°F) if cumulative industrial-era fossil fuel emissions are limited to 500 GtC (gigatons of carbon, where a gigaton is one billion metric tons) and if policies are pursued to restore 100 GtC into the biosphere, including the soil. This scenario leads to reduction of atmospheric CO2 to 350 ppm by 2100, as needed to restore Earth's energy balance and approximately stabilize climate.

Awakening the Sleeping Giant of Climate Skepticism

by Joanna Benn 

This Friday, the widely anticipated and long-awaited state of the Earth and its climate will be released by the UN’s climate assessment body, the IPCC. In a pre-emptive strike, the right wing media last week launched a full front attack to discredit the climate science using leaked drafts. In the past week, we've seen a host of vitriolic ‘they got it all wrong’ stories ranging from the Mail on Sunday to Rupert Murdoch's The Australian and the Wall Street Journal.

For most of us, being non-climate scientists, it is confusing to make sense of the facts and counter- arguments. If one takes out opinion and ideology and leaves it to the scientists, which seems a good strategy to me– the next stage for climate skeptics is to discredit them. I don’t understand this. I don’t comment on medical advances as I am not a doctor, but it appears that everyone is an expert on climate change. If 97 doctors cite one diagnosis and three others have a different opinion, it’s likely I will believe the majority. If weather forecasters tell me there is a 90 percent chance of rain in the morning, I will probably take an umbrella with me.

These climate skeptic journalists, working from leaked incomplete versions of the report, apparently know more than the 830 expert authors from 85 countries who have in large part, dedicated their lives to this work. Working Group 1, which is the first part of the report due out next week, summarizes the Physical Science IE. What’s happening to the ocean, atmosphere, ice-caps and beyond. It uses findings gained from new technology which like all things in our increasingly IT-led world, have moved with incredible speed.

Satellites in the sky, buoys floating in the ocean and ice cores that provide a carbon record from far back in Earth’s history are all part of the sophisticated armory used. Alongside this progress, computing advances now allow for increasingly realistic and reliable models of the climate. So, scientists are able to examine the complex physical, chemical and biological processes that influence the Earth’s climate in finer detail than ever before. In addition they can project how it will change as a result of human activities.

If climate skeptics really want to properly engage in the debate, surely the time is when the results are released and final. To me it seems a cheap shot to go in ahead of time and present skewed, selective findings when the scientists in questions can’t respond publicly until the embargo lifts.

1. If you’re interested in some strong rebuttal to the media, Carbon Brief in the UK is an excellent source of information: http://www.carbonbrief.org/blog/2013/09/scientists-take-the-mail-on-sunday-to-task-over-claim-that-warming-is-half-what-ipcc-expected/

2. Here, Dana Nuccitelli takes apart David Rose's earlier claims that the Arctic has recovered from its melting phase. http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/sep/09/climate-change-arctic-sea-ice-delusions

3. Twelve prominent climate scientists and experts from across the globe state that "the body of evidence is overwhelming" and that dangerous climate change is happening. The full statement can be found here.

4. And in Germany, this strong editorial made the front page saying, “The empirical evidence for accelerated climate change is strong. Yet many still call it into question or dismiss it as scientific mumbo-jumbo that should be filed away and forgotten. These individuals obscure one thing in particular: their own interests."

In a few days, governments and scientists from around the globe will agree and sign off the executive summary of this new report. Perhaps we should all just sit tight and wait to see what it says; then think about what needs to be done to keep the global average temperature rise at less than 2°C above pre-industrial levels. Surely that, and not the current war of words, is the important part.