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«Major points: Recent data and research supports the importance of natural climate variability and calls into question the conclusion that humans are ...»

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10 Lewis, N. and J.A. Curry, (2014) The implications for climate sensitivity of AR5 forcing and heat uptake. Climate Dynamics http://link.springer.com/article/10.1007%2Fs00382-014-2342-y#page-1 11 Stevens, B (2015) Rethinking the lower bound on aerosol forcing. J. Climate, http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00656.1 12 A revised version of Figure 11.25 from the AR5 WG1 Report is given by Ed Hawkins at http://www.climate-labbook.ac.uk/comparing-cmip5-observations/ Based upon climate model projections, the probability of the hiatus extending beyond 20 years is vanishing small. The warming hiatus, combined with assessments that the climate-model sensitivities are too high, raises serious questions as to whether the climate-model projections of 21st century

temperatures are fit for supporting public policy decisions:

• Are climate models too sensitive to greenhouse forcing?

• Is modeled treatment of natural climate variability inadequate?

• Are model projections of 21st century warming too high?

Whither the 21st century climate?

The issue of greatest concern is how the climate will evolve during the 21st century. There are two different views on this.

The first perspective is that of the IPCC, which projects continued warming through the 21st century, and is expected to surpass the ‘dangerous’ threshold of 2°C warming as early as 2040. The figure below, from the IPCC AR5 Summary for Policy Makers, shows climate model projections of 21st century warming, with RCP8.5 reflecting ‘business as usual’ emissions of greenhouse gases.

The other perspective emphasizes natural variability:

• Our understanding of circulation regimes in the Atlantic and Pacific Oceans (stadium wave hypothesis)13 suggests that the ‘hiatus’ will continue at least another decade, perhaps into the 2030’s. Arctic sea ice will recover over the next two decades.

• Climate models are too sensitive to human forcing; 21st century warming will be on the low end of IPCC projections (or even below).

• Solar variations and volcanic eruptions are a wild card. Russian scientists14 argue that there was a Grand Solar Maximum that peaked in the late 20th century, and that we can expect a Grand Solar Minima (contributing to cooling) to peak around 2060.

• And finally, we can’t rule out unforeseen surprises. The hiatus in warming in the early 21st century was an unforeseen surprise.

Time will tell which of these two perspectives is correct.

Summary Anthropogenic climate change is a theory in which the basic mechanism is well understood, but the potential magnitude is highly uncertain. We know that the climate changes naturally on decadal to century time scales, but we do not have explanations for a number of observed historical and paleo- climate variations, including the warming from 1910-1940, the mid-20th century cooling and the 21st century hiatus in warming. Disagreement regarding climate change arises from our recognized uncertainty regarding natural climate variability.

Climate model projections of the 21st century climate are losing credibility because of:

• Failure to predict the early 21st century hiatus in surface warming

• Inability to simulate the patterns and timing on multidecadal ocean oscillations

• Lack of account for future solar variations and solar indirect effects on climate

• Apparent oversensitivity to increases in greenhouse gases So, how will the 21st century climate evolve? Apart from lack of confidence in climate model projections that focus primarily on the impact of increases in greenhouse gases, we don’t have sufficient understanding to project solar variations, future volcanic eruptions and decadal to century variations in deep ocean circulations. We can't rule out a continuation of the warming hiatus, or even cooling during parts of the 21st century. How solar variations, volcanic eruptions, ocean circulations and human influences will interact to determine the evolution of the 21st century climate is not known with any confidence, and scientists disagree as to which of these factors will dominate.

The climate change response challenge

Claims that the earth has been warming, that there is a greenhouse effect, and that man’s activities have contributed to warming, are trivially true, but they are essentially meaningless by themselves in terms of alarm. These truths also do not mandate a specific policy response.

13 Wyatt, MG and JA Curry, 2013: Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century. Climate Dynamics, http://curryja.files.wordpress.com/2013/10/stadium-wave1.pdf 14 Abdussamatov, H 2013: Current long-term negative energy balance of the earth leads to the new little ice age. Journal of Geology and Geophysics http://omicsgroup.org/journals/grand-minimum-of-the-total-solar-irradiance-leads-to-the-little-iceage-2329-6755.1000113.pdf Is climate change dangerous?

Central to responding to climate change is this question: Is warming ‘dangerous’? The UN Framework Convention on Climate Change (UNFCCC) international environmental treaty (1992) states as its objective:15 “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” The IPCC 3rd and 4th Assessment reports refer to ‘reasons for concern.’ It wasn’t until 2010 that some clarification of ‘dangerous’ was provided by UN international negotiators:16 “In 2010, governments agreed that emissions need to be reduced so that global temperature increases are limited to below 2 degrees Celsius.” The target of 2oC remains the focal point of international agreements and negotiations, although this definition remains controversial and is being challenged.





The original rationale for the 2oC target is the idea that ‘tipping points’ - abrupt or nonlinear transition to a different state - become likely to occur once this threshold has been crossed, with consequences that are largely uncontrollable and beyond our management. The IPCC AR5 considered a number of potential tipping points, including ice sheet collapse, collapse of the Atlantic overturning circulation, and permafrost carbon release. Every single catastrophic scenario considered by the IPCC (Table 12.4) has a rating of very unlikely or exceptionally unlikely and/or has low confidence. The only tipping point that the IPCC considers likely in the 21st century is disappearance of Arctic summer sea ice (which reforms each winter, in any event).

In the absence of tipping points on the timescale of the 21st century, the 2oC limit is more usefully considered by analogy to a highway speed limit:17 driving at 10 mph under the speed limit is not automatically safe, and exceeding the limit by 10 mph is not automatically dangerous, although the faster one travels the greater the danger from an accident. Analogously, the 2oC limit should not be taken literally as a real danger threshold.

Nevertheless, the 2oC limit is used politically to motivate the urgency of action to reduce CO2 emissions.

At a recent UN Climate Summit, Secretary-General Ban Ki-moon warned that: “Without significant cuts in emissions by all countries, and in key sectors, the window of opportunity to stay within less than 2 degrees [of warming] will soon close forever.”18 Actually, this window of opportunity may remain open for quite some time. The implications of the lower values of climate sensitivity found by Lewis and Curry and other recent studies is that human-caused warming is not expected to exceed the 2oC ‘danger’ level in the 21st century. A slower rate of warming means there is less urgency to phase out greenhouse gas emissions now, and more time to find ways to decarbonize the economy affordably. It also allows us the flexibility to revise our policies as further information becomes available.

Is it possible that something really dangerous and unforeseen could happen to Earth’s climate during the 21st century? Yes it is possible, but natural climate variability (perhaps in conjunction with human-caused climate change) may be a more likely source of possible undesirable change than human causes. In any event, attempting to avoid such a dangerous and unforeseen climate by reducing fossil fuel emissions will be futile if natural climate is a dominant factor.

15 http://unfccc.int/essential_background/convention/items/6036.php 16 http://unfccc.int/essential_background/items/6031.php 17 http://www.carbonbrief.org/blog/2014/12/two-degrees-a-selected-history-of-climate-change-speed-limit/ 18 http://newsroom.unfccc.int/unfccc-newsroom/un-climate-summit-ban-ki-moon-final-summary/ Biased information cascades Climate change may exacerbate environmental problems that are caused by overpopulation, poorly planned land-use and over-exploitation of natural resources. However, it is very difficult to separate out the impacts of human caused climate change from natural climate change and from other societal impacts.

Nevertheless, climate change has become a grand narrative in which human-caused climate change has become a dominant cause of societal problems.19 Everything that goes wrong, and even pre-existing concerns, reinforces the conviction that that there is only one thing we can do prevent societal problems – stop burning fossil fuels. This grand narrative misleads us to think that if we solve the problem of climate change, then these other problems would be ameliorated.

Politicians, activists and journalists have stimulated a biased information cascade of alarm about humancaused climate change to support a political agenda of reducing fossil fuel emissions. An information cascade is a self-reinforcing process of collective belief formation that triggers a self-perpetuating chain reaction as a band wagon or snowballing process: the more attention a danger gets, the more worried people become, leading to more news coverage and greater alarm. Because slowly increasing temperatures don’t seem alarming, the cascade facilitators push extreme weather events and public health impacts as being caused by human-caused climate change, more of which is in store if we don’t quickly act to cool the planet by reducing fossil fuel emissions.

A deconstruction of this information cascade is needed to avoid bias in our thinking and to better

understand the true risks of human caused climate change:

• The basis for this cascade originates from the 1992 UNFCCC treaty, to avoid dangerous human caused climate change through stabilization of CO2 emissions. Note, it was not until 1995 that the IPCC 2nd Assessment Report identified a ‘discernible’ human influence on global climate.

The policy ‘cart’ was clearly leading the scientific ‘horse.’

• Then, the UNFCCC changed the definition of climate change to refer to a change of climate that is attributed directly or indirectly to human activity. This leads to the perception that all climate change is caused by humans.

• Sea level rise and extreme weather events such as hurricanes, drought and heat waves are attributed to climate change, which is assumed de facto to be caused by humans.

• Human health impacts, national security risks, etc. that are exacerbated by extreme weather events are then fallaciously inferred to be caused by human-caused climate change.

A critical link in this cascade is the link between human-caused climate change and extreme weather. In 2012, the IPCC published a Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX).20 The Report found low to medium confidence of a trend in droughts in some regions and the frequency of heavy rains in some regions, and high confidence of a trend in heat waves in Australia. There is no trend in hurricanes or wild fires. Attribution of any trend in extreme weather events to human caused climate change cannot be done with any confidence. With regards to the perception (and damage statistics) that severe weather events seem more frequent and more severe over the past decade, there are several factors in play. The first is the increasing vulnerability and exposure associated with increasing concentration of wealth in coastal and other disaster-prone regions.

The second factor is natural climate variability. Many extreme weather events have documented relationships with natural climate variability; in the U.S., extreme weather events (e.g. droughts, heat waves and hurricanes) were significantly worse in the 1930’s and 1950’s.21 19 Korhola, E-R 2015 Climate change as a political process https://helda.helsinki.fi/bitstream/handle/10138/136507/Therisea.pdf?sequence=1 20 IPCC SREX http://www.ipcc-wg2.gov/SREX/ 21 Curry, JA 2014 Senate EPW testimony http://judithcurry.com/2014/01/16/senate-epw-hearing-on-the-presidents-climateaction-plan/ The information cascade of climate change as apocalypse is impeding our ability to think rationally about how we should respond to climate change, and acts to narrow the viewpoints and policy options that we are willing to consider in dealing with complex issues such as public health, weather disasters and national security. Should we be surprised when reducing CO2 emissions does not ameliorate any of these problems?

Wrong trousers: climate change as a wicked problem

In the decades since the UNFCCC Treaty and the Kyoto Protocol, global emissions have continued to increase, especially in developing countries. UN Climate Conferences have not produced a new treaty in this framework. Opposition to a new treaty arises from concerns over economic costs and the need to ameliorate energy poverty in less developed countries. A key issue in the climate policy debate is whether the proposed ‘cure’ (i.e. CO2 emissions reduction and associated economic hardships) is worse than the ‘disease’ (i.e. warmer temperatures).

In their Wrong Trousers essay,22 Prins and Rayner argue that we have made the wrong cognitive choices in our attempts to define the problem of climate change and its solution, by relying on strategies that worked previously for ‘tame’ problems. A tame problem is well defined, well understood, and the appropriate solutions are agreed upon. Cost-benefit analyses and mitigation techniques are appropriate for tame problems, and the potential harm from miscalculation is bounded.



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