Published in the journal Climate Risk Management today, our research is the first to quantify the probability of historical changes in global temperatures and examines the links to greenhouse gas emissions using rigorous statistical techniques.

There is less than 1 chance in 100,000 that global average temperature over the past 60 years would have been as high without human-caused greenhouse gas emissions, our new research shows.

Published in the journal Climate Risk Management today, our research is the first to quantify the probability of historical changes in global temperatures and examines the links to greenhouse gas emissions using rigorous statistical techniques.

Our new CSIRO work provides an objective assessment linking global temperature increases to human activity, which points to a close to certain probability exceeding 99.999%.

Our work extends existing approaches undertaken internationally to detect climate change and attribute it to human or natural causes. The 2013 Intergovernmental Panel on Climate Change Fifth Assessment Report provided an expert consensus that:

It is extremely likely [defined as 95-100% certainty] that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic [human-caused] increase in greenhouse gas concentrations and other anthropogenic forcings together.

Decades of extraordinary temperatures

July 2014 was the 353rd consecutive month in which global land and ocean average surface temperature exceeded the 20th-century monthly average. The last time the global average surface temperature fell below that 20th-century monthly average was in February 1985, as reported by the US-based National Climate Data Center.

This means that anyone born after February 1985 has not lived a single month where the global temperature was below the long-term average for that month.

We developed a statistical model that related global temperature to various well-known drivers of temperature variation, including El Niño, solar radiation, volcanic aerosols and greenhouse gas concentrations. We tested it to make sure it worked on the historical record and then re-ran it with and without the human influence of greenhouse gas emissions.

Our analysis showed that the probability of getting the same run of warmer-than-average months without the human influence was less than 1 chance in 100,000.

We do not use physical models of Earth’s climate, but observational data and rigorous statistical analysis, which has the advantage that it provides independent validation of the results.

Detecting and measuring human influence

Our research team also explored the chance of relatively short periods of declining global temperature. We found that rather than being an indicator that global warming is not occurring, the observed number of cooling periods in the past 60 years strongly reinforces the case for human influence.

We identified periods of declining temperature by using a moving 10-year window (1950 to 1959, 1951 to 1960, 1952 to 1961, etc.) through the entire 60-year record. We identified 11 such short time periods where global temperatures declined.

Our analysis showed that in the absence of human-caused greenhouse gas emissions, there would have been more than twice as many periods of short-term cooling than are found in the observed data.

There was less than 1 chance in 100,000 of observing 11 or fewer such events without the effects of human greenhouse gas emissions.

Good risk management is all about identifying the most likely causes of a problem, and then acting to reduce those risks. Some of the projected impacts of climate change can be avoided, reduced or delayed by effective reduction in global net greenhouse gas emissions and by effective adaptation to the changing climate.

Ignoring the problem is no longer an option. If we are thinking about action to respond to climate change or doing nothing, with a probability exceeding 99.999% that the warming we are seeing is human-induced, we certainly shouldn’t be taking the chance of doing nothing.

The Conversation

The authors do not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article. They also have no relevant affiliations.

This article was originally published on The Conversation.
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  1. Gee, it is nice to see some well considered comments instead of the more typical PC inflamed responses on the subject.

  2. Do we have an EROEI figure for a coal (brown or black) fired power station? Does this EROEI figure referred to above take into account the ash and CO2,CH4 etc. produced by solar and wind powered systems?

    1. Coal is about 30, nuclear about 100.

  3. If all the above is true, why do you insist on promoting solar and wind renewables? Knowing that they cannot supply a sufficient energy return on energy invested? I refer you to the following article on the Brave New Climate website:
    “The focus then moves to EROEI, possibly the most important metric to consider in energy system transformation. It takes energy to build any kind of power plant, so the plant had better be able to give at least that much energy back before it wears out, or the game isn’t worth the candle.

    If the energy returned just balances the energy used to create it, the power plant has an EROEI of 1. It’s breakeven. And that’s not enough, because it also has to supply energy for the society that builds it. It has to power not just the construction of more power plants, but the homes, roads, schools, hospitals, clothes, cars, computers, armies, movie theatres, farms and all the elements of the civilization in which it is embedded.

    There is a minimum EROEI required for an energy source to be able to support our present civilization. For countries like the US and Germany, this is estimated to be about 7. An energy source with lower EROEI cannot sustain a civilization at that level of complexity, structured along similar lines. If we are to transform our energy system, in particular to one without climate impacts, we need to pay close attention to the EROEI of the end result.

    And here an analysis of the EROEI of solar leads to an uncomfortable conclusion: adding storage to solar PV reduces the EROEI, to just above 2. This is not enough net energy to be a viable energy source. Weißbach et al. found a similar result for wind, reporting an EROEI of 3.9 for wind with storage, below the viable threshold of 7. So the idea that advances in energy storage will enable renewable energy is a chimera – the Catch-22 is that in overcoming intermittency by adding storage, the net energy is reduced below the level required to sustain our present civilization.”

  4. What you may have shown is that there is a near certainty that measured global temperatures have increased in this period. Fair enough.

    However, what you have not shown is that it is due to AGW. You’ve simply ASSUMED, like the IPCC, that this rise is due to the (measured) increasing levels of the greenhouse gas CO2. This entirely unproved assumption does not come from any measurements.

    Correct me if I’m wrong in my deduction. In fact, can you show that changing levels of CO2 above ca 140ppm can cause any change to global warming? (That level of 140ppm comes from ground-based IR measurements.)

    If, as you write,
    “Our analysis – as well as the work of many others – shows beyond reasonable doubt that humans are contributing to significant changes in our climate.”
    you should have no difficulty in coming up with that evidence.

  5. I do believe in Global Warming, although humans do contribute I fail to see that modern day usage of Fossil Fuels would be the “Main cause.”

    The Industrial Revolution start around 1570 & the mining & large scale burning of Dirty Coal from thence to the 1860’s would have produced much more CO2 than is emitted nowadays. By enlarge Liquid Hydrocarbons have taken the place of Coal. The technology has improved in the 20/21st. Century so the out put of CO2 by industry is actually down on the previous 3 Centuries. The increase in Population has to be taken into account & that would negate some of the drop.

    There should have been a Global Warming in the 17th. Century except the very opposite happened with a mini Ice Age happening in Europe.

    I do believe that Alternate Fuels & Energy Storage will eventually replace half of Fossil Fuel, if not more, in the future. There will always be a lag time for the introduction of any new Technology.

    The heightened anxiety of Green Groups is the main hindering point to the introduction of New Technology. They put peoples back up so they will refuse to move in the face bombastic behaviour & of course, the Fossil Fuel Industry CEO’s don’t want to lose the lucrative incomes.

    The Fossil Fuel Industry does employ a lot of people who stand to lose the employment. A sudden stop of Fossil Fuels would not do anybody any good. Wars would start, disease & famine would follow. OK, the benefit of that would be a reduced World Population.

    If humans didn’t exist would the roaming herds of grazing animals produced the same amount of CO2? difficult question.

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