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ECON*2100 Economic Growth and Environmental Quality Climate Change Lectures I. Science Background 1 Slogans versus Evidence • There is no area of public policy where the reliance on dogmatic slogans instead of real evidence has become so problematic • The worst perpetrators are usually public officials who are thought to have special expertise or decision-making responsibility 2 Examples • Gord Miller, former Ontario Environment Commissioner http://eco.on.ca/2014-ghg-looking-for-leadership/ 3 Examples • President Obama: “[w]hat we do know is the temperature around the globe is increasing faster than was predicted even ten years ago” (press conference, November 14 2012, reported in Washington Post, 2012); 4 Examples • Gina McCarthy, US EPA Administrator 5 Examples • Gina McCarthy, US EPA Administrator “climate change is driven, in large part, by carbon pollution, and it leads to more extreme heat, cold, storms, fires and floods. For farmers who are strained by the drought, for families with homes in the path of a wildfire, for small businesses along our coastlines, climate change is indeed very personal… Scientists are as sure that humans are causing climate change as they are that cigarette smoke causes lung cancer.” 6 So… • Climate change is accelerating and is going faster than model predictions • Greenhouse gas emissions are clearly linked to increasing trends in storms, droughts, extreme weather, etc. • But is any of this true? 7 IPCC (2013) on the slowing down of global warming • “Despite the robust multidecadal timescale warming, there exists substantial multi-annual variability in the rate of warming with several periods exhibiting almost no linear trend (including the warming hiatus since 1998).” • (IPCC, 2013: Chapter 2, page 39; emphasis added) 8 IPCC (2013) on model over-estimation • IPCC Ch. 9: 111 out of 114 models predicted too much warming since late 1990s • Fyfe et al. (2013) GCM trends averaged 0.21 oC/decade, more than 4x observed level rossmckitrick.com 9 IPCC (2012) on Extreme Weather • In the US “droughts have become less frequent, less intense or shorter.” • Worldwide there is only “limited to medium” regional evidence regarding changes in floods because the records are sparse and the effects are confounded with changes in land use and engineering. “Furthermore there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes.” “There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases.” But “Attribution of single extreme events to anthropogenic climate change is challenging.” • • 10 So… • Global warming is slowing down, not accelerating • Models over-predicted warming over past 2 decades • Few identifiable trends in weather extremes and little solid connection to GHG emissions 11 What do we mean by “global warming”? • “Since the late 1960s, much of the North Atlantic Ocean has become less salty, in part due to increases in fresh water runoff induced by global warming, scientists say." -Michael Schirber, LiveScience June 29, 2005 • “The surface waters of the North Atlantic are getting saltier, suggests a new study of records spanning over 50 years. They found that during this time, the layer of water that makes up the top 400 metres has gradually become saltier. The seawater is probably becoming saltier due to global warming, Boyer says.“ -Catherine Brahic, New Scientist August 23, 2007 12 The Greenhouse Effect • The sun sends energy to the Earth • The Earth has to send it all back to space 13 The Greenhouse Effect • 2 ways energy leaves the Earth’s surface: • Convection • Radiation 14 Convection • Process that creates weather • Warm, wet air rises • Cool, dry air from above comes down • Rain and wind cool the surface 15 Radiation • The Earth is like a light bulb • The light is too dim for our eyes to see • “Infrared Radiation” 16 Different Proportions • Stratosphere: – Mostly radiation • Surface & troposphere: – Convection & radiation 17 The Greenhouse Effect • The sun sends energy to the Earth • The Earth has to send it all back to space convection radiation 18 The Greenhouse Effect • Some gases absorb infrared light and warm up – – – – Water Vapour Carbon dioxide (CO2) Methane A few others • Water Vapour does 95% of the absorption 19 What happens when we burn fossil fuels? • The amount of CO2 in the air is going up a little each year 20 The Greenhouse Effect • The sun sends energy to the Earth • The Earth has to send it all back to space convection radiation • Now some more of the infrared energy is absorbed 21 The problem… • While the radiative changes are relatively straightforward to model (linear)… • Convection, or fluid dynamics, are very difficult to model (highly nonlinear) • Consequently the problem can only be analyzed using empirical approximations 22 What do people agree on? • CO2 is a greenhouse gas (infrared absorbing) • CO2 concentration in the atmosphere is going up due to fossil fuel use • All other things being, this is likely to cause an increase in temperatures • Since the early 1800s, the world has warmed • Changes due to CO2 are relatively small: large changes require large feedback processes to kick in 23 Where are the disagreements? • Feedbacks and amplification mechanisms – Models versus observations • Whether natural variability explains some or most of modern climate changes • Whether the changes are harmful or not 24 97% Consensus? • Obama 2013: “97% of scientists agree climate change is real, manmade and dangerous” – Survey questions: Is CO2 a greenhouse gas, and do human activities contribute to climate change? – 77 out of 79 agreed – “97% of scientific papers say…” In fact the majority (66%) took no position, 33% accept at least a weak role for GHG’s – 2012 American Meteorological Society survey: only 52% agreed humans responsible for most recent global warming 25 Long Term Context • The climate varies naturally on long and short time scales Long Term Context • CO2 levels vary too Modern Warming in Context • Ice core record 420,000 years 28 The world’s longest thermometer record – Central England – 1650 to 2013 29 Modern warming: pattern • Surface air temperature averages are typically used • Also tropospheric air temperature, sea ice, etc. • Major regions: – Land – Ocean – Northern Hemisphere – Southern Hemisphere 30 Land record sample size • Collapsing sample size 31 Land record sample size • Growing bias towards airports 32 33 34 35 ross.mckitrick.googlepages.com 36 ross.mckitrick.googlepages.com 37 38 Land and Ocean Land Ocean 39 NH and SH Sea Ice 1979 – 2013 40 Is there a problem? • [Present] emission trends put the world plausibly on a path toward 4°C warming within this century. Levels greater than 4°C warming could be possible… Current scientific evidence suggests that even with the current commitments and pledges fully implemented, there is roughly a 20 percent likelihood of exceeding 4°C by 2100, and a 10 percent chance of 4°C being exceeded as early as the 2070s. – Potsdam Institute for Climate Studies 41 Is there a problem? • The only sure thing is what we have so far been able to measure…The warming we have had over the last a 100 years is so small that if we didn’t have had meteorologists and climatologists to measure it we wouldn’t have noticed it at all… It indicates that the climate sensitivity is probably lower than climate models, at least initially adopted. – Lennart Bengtsson, European Weather Centre, Head of Atmospheric and Space Science Institute, Bern 42 Is there a problem? • Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia…Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system…It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. 43 Is there a problem? • The IPCC iconic statement that there is a high degree of certainty that most of the warming of the past 50 years is due to man’s emissions is, whether true or not, completely consistent with there being no problem. To say that most of a small change is due to man is hardly an argument for the likelihood of large changes. – Richard Lindzen, Meteorologist, MIT 44 Amplification mechanisms • Water vapour feedback – As air warms it can hold more moisture – Add a little CO2 – Air warms a little – H2O level rises – Air warms a lot 45 Amplification mechanisms • Ice-albedo feedback – “albedo” = reflectivity of surface – Snow-covered ice is highly reflective – Ocean surface is much less so – If polar regions warm, sea ice retreats a bit – Oceans then absorb more solar energy, warming more 46 Feedbacks • Without feedbacks, doubling CO2 would warm up surface in a simple climate model by about 1C 47 Feedbacks • IPCC projects CO2 doubling (going from 280 ppm to 560 ppm) will cause 1.5 – 4.5 C warming • In other words, feedbacks are strongly positive 48 Feedbacks • The scientific problem: – Feedbacks cannot be resolved from basic physics or first principles – They have to be simulated in numerical models then tested empirically – Small uncertainties in feedbacks translate into large uncertainties in forecasts 49 Testing Feedbacks • Tropical Troposphere • Equilibrium Climate Sensitivity 50 Tropical Troposphere Most rapid warming is expected to occur in 2 regions: - tropical troposphere - polar surfaces 51 Tropical Troposphere • • • • • Half the planetary atmosphere Most incoming solar energy enters climate there High humidity = abundant water vapour 55% of amplification effect occurs here in models Temp’s monitored by weather balloons since 1958, satellites since 1979 52 Tropical Troposphere • The problem: Not much warming there despite CO2 levels going up 18% since 1979 Current Model Spread Current Observations 53 Tropical Troposphere • Since 1958, CO2 up by 30% • Except for step change in 1978, no trend in midtroposphere; almost no change in lower troposphere • Models predict far too much warming 54 Tropical Troposphere • Models • Balloons Satellites 55 ECS • Equilibrium Climate Sensitivity • Amount of warming in a model after instantaneously doubling CO2 level, and then allowing all processes to come to equilibrium • Traditional range: 1.5 – 4.5 deg C • But models can show much higher top end 56 ECS • Using simplified models the distribution is very wide • Roe & Baker, Science 2007 57 ECS • But recent empirical studies have yielded estimates at or near the bottom end: – Lewis, N. (2013): ECS best estimate 1.64 °𝐂, likely range 1.3 – 2.2 °C – Lewis, N. and Curry, J. (2014) ECS best estimate 1.64 °C, likely range 1.1 – 4.1°C – Aldrin, M. et al (2012): ECS best estimate 1.76 °𝐂, likely range 1.3 – 2.5 °C – Ring, M.J. et al. (2012): ECS best estimate 1.80 °𝐂, likely range 1.4 – 2.0 °C. (Note ECS falls to 1.6 °𝐂 if HadCRUT3 temperature data is replaced by HadCRUT4.) – Otto, A., et al., (2013): ECS best estimate 1.91 °C, likely range 1.3 – 3.0 °C – Masters, T. (2013): ECS best estimate 1.98 °𝐂, likely range 1.2 – 5.2 °C – Loehle, C. (2-14): ECS best estimate 1.99 °𝐂, likely range 1.7 – 2.2 °C – Johanssen et al. (2015): ECS best estimate 2.50 °𝐂, likely range 2.0 – 3.2 °C 58 ECS • But recent empirical studies have yielded estimates at or near the bottom end: – Lewis, N. (2013): ECS best estimate 1.64 °𝐂, likely range 1.3 – 2.2 °C – Lewis, N. and Curry, J. (2014) ECS best estimate 1.64 °C, likely range 1.1 – 4.1°C – Aldrin, M. et al (2012): ECS best estimate 1.76 °𝐂, likely range 1.3 – 2.5 °C – Ring, M.J. et al. (2012): ECS best estimate 1.80 °𝐂, likely range 1.4 – 2.0 °C. (Note ECS falls to 1.6 °𝐂 if HadCRUT3 temperature data is replaced by HadCRUT4.) – Otto, A., et al., (2013): ECS best estimate 1.91 °C, likely range 1.3 – 3.0 °C – Masters, T. (2013): ECS best estimate 1.98 °𝐂, likely range 1.2 – 5.2 °C – Loehle, C. (2-14): ECS best estimate 1.99 °𝐂, likely range 1.7 – 2.2 °C – Johanssen et al. (2015): ECS best estimate 2.50 °𝐂, likely range 2.0 – 3.2 °C 59 Model-Observation Discrepancy IPCC AR5 report 60 Model-Observation Discrepancy • IPCC AR5, Box 9.2 Figure 1 • Note middle panel begins with volcano and ends with an El Nino 61 Model-Observation Discrepancy • ‘The growing divergence between climate model simulations and observations raises the prospect that climate models are inadequate in fundamental ways,’ – Judith Curry, Climatologist, Chair of Earth and Atmospheric Sciences, Georgia Tech 62 Model-Observation Discrepancy • “If things continue as they have been, in five years, at the latest, we will need to acknowledge that something is fundamentally wrong with our climate models…A 20-year pause in global warming does not occur in a single modeled scenario. But even today, we are finding it very difficult to reconcile actual temperature trends with our expectations.” – Hans von Storch, Climatologist , GKSS, Germany (2013) 63 Conclusions • The basic points on which there is wide scientific agreement establish that humans can, and likely do, influence the climate system by raising the atmospheric CO2 fraction • On its own this is not enough to prove that the changes pose a problem, or even will be large enough to notice • Making that argument requires additional assumptions about positive (amplifying) feedbacks, as represented in computer models of the climate system 64 Conclusions • A lot of credible scientists working on the problem believe the positive feedbacks are large enough to pose problems in the years ahead • But key discrepancies between models and observations are raising the likelihood that models overstate the feedbacks and the sensitivity of the climate system to CO2 emissions • The next 4-5 years will likely suffice to settle this debate 65 Conclusions • Science is always about the weight of the evidence. Few things are provable in an absolute sense. One must always be open to surprises, reinterpretations, and the possibility that one has been wrong … • Climate change presents us with one of the most difficult of all scientific problems, heavily encumbered with the need to make political and economic decisions long before hard evidence is at hand. – Carl Wunsch, Professor of Physical Oceanography, MIT 66