Tag Archives: IPCC

Climate Change Will Make ISIS Look Like Amateurs

The destruction by ISIS (Islamic State) of the ancient Assyrian city of Nimrud in Iraq and potential destruction of Palmyra in Syria has shocked the world—almost as much as the organisation’s previous beheadings of its captives.

Nimrud jpeg

Unfortunately, an article in this week’s New Scientist on sea level rise titled “Five Metres and Counting” (apologies print or paywall access only) suggests that climate change has already committed the world to the destruction of human heritage many orders of magnitude greater than anything ISIS is capable of doing.

You may be familiar with the Intergovernmental Panel on Climate Change (IPCC)‘s end of century sea level rise forecast (here, page 11 in the report). This pegs the upper sea level rise outcome at just below one metre (click for larger image).

IPCC Sea Level jpeg

What is less well-known is that this is just the preliminary phase of sea level rise. Given the extent of warming to date plus the warming guaranteed by current levels of carbon dioxide in the atmosphere, we are committed to barrel through one metre. In the words of Michael Le Page from The New Scientist:

Whatever we do now, the seas will rise by at least 5 metres. Most of Florida and many other low-lying areas and cities around the world are doomed to go under. If that weren’t bad enough, without drastic cuts in global greenhouse gas emissions–more drastic than any being discussed ahead of the critical climate meeting in Paris later this year—a rise of 20 metres will soon be unavoidable.

The arithmetic is pretty depressing (chart from New Scientist article): 0.4 metres for mountain glaciers, plus 0.8 metres for ocean thermal expansion, plus 3.5 metres for the West Antarctic ice sheet (the areas in orange in the chart below, click for larger image). If we go past 2 degrees Celsius of warming and get to 4 degrees, then we add all the blue bars as well.

NS Meltdown Imminent jpeg

Since the IPCC’s Fifth Assessment Report (AR5) was published, fresh evidence has emerged relating to West Antarctic ice sheet instability. Moreover, two large basins, the Aurora and the Wilkes, that form part of the East Antarctic ice sheet also appear vulnerable. In short, if we push up to 4 degrees Celsius of warming, then we are likely committing ourselves to 20 metre sea level rise.

So we’ve seen what ISIS had done in Nimrud, this is what we will do to Venice with 20 metres of sea level rise (source: here):

Venice jpeg

And New York:

New York jpeg

These projections are Old Testament in terms of the scale of the catastrophes they portend; indeed, ISIS could only dream of unleashing such wanton destruction. Yet, in our failure to tackle climate change, such wanton destruction appears to have been accepted by the G20 elites and, frankly, ourselves.

Addendum: 

Had a request for the background papers quoted by New Scientist. Most of these are behind paywalls but the authors frequently make pdfs available on their personal web sites or the web sites of their institutions:

Link to Science article on collapse of West Antarctic ice sheets
http://sumnerscience.com/wp-content/uploads/2014/05/Science-2014-Sumner-683.pdf

Link to Nature Geoscience article on Aurora Basin (East Antarctic): http://www.nature.com/ngeo/journal/v8/n4/full/ngeo2388.html

Link to Nature Climate Change article on Wilkes (East Antarctic):
http://www.nature.com/nclimate/journal/v4/n6/full/nclimate2226.html

Link to Earth and Planetary Science Letters on overall East Antarctic melting (total 15 metres):
http://www.sciencedirect.com/science/article/pii/S0012821X14007961

Link to Nature Climate Change Letter on Greenland
http://www.nature.com/nclimate/journal/v2/n6/full/nclimate1449.html

Chart of the Day, 30 Jan 2015: Pick a Pathway (to Climate Nirvana or Climate Hell)

After yesterday’s post on China’s emissions, I will try to keep in a ‘cup half full’ frame of mind today.

The Intergovernmental Panel on Climate Change (IPCC) is an organisation for which I have great respect. But while their research may be applauded for its rigour,  communication with the wider world frequently lacks clarity (to put it mildly). Take, for example, the emissions scenarios, which in the Fifth Assessment Report (AR5) are called Representative Concentration Pathways (RCPs). Here are the RCPs and the change in temperature that accompanies them (Source: IPCC AR5, WG1).

Global Mean Temperature Change jpeg

I have spent many an hour grinding through IPCC reports trying to find clear explanations of what sits behind these pathways, but it is a painful process. Eventually, Skeptical Science saved the day by publishing “The Beginner’s Guide to Representative Concentration Pathways“.

There are four Representative Concentration Pathways: RCP 8.5, RPC 6, RCP 4.5 and RCP 2.6. The numbers refer to what is termed the ‘radiative forcing’, the change in net energy flow as measured in watts per square metre. Moreover, RCP 8.5 is expected to keep on increasing past 2100, RCP 6 and 4.5 will peak in 2100 and RCP 2.6 will have peaked prior to 21oo. Simplistically, a larger forcing means the globe will reach a higher mean temperature, as you can see in the chart above.

Surprisingly, AR5 is not particularly concerned with the socioeconomic assumptions that lie behind the RCPs. In this respect, the climate scientists behind the RCP concept are thinking the way economists often do: they are saying “imagine if we had condition X, what would be the output Y”. In this way, you can explore the model, and, hopefully, you obtain some insight which you can then take back to the real world.

I’m still a little uncomfortable with this. I think the IPCC should have chosen RCPs with highly transparent assumptions and realistic story lines. Instead, two of the four RCPs look utterly unrealistic to me. For example, to get to RCP 2.6 would require a transition away from fossil fuels that now looks impossible. And the good news? Well, RCP 8.5 looks barking mad to me too. Here are the emissions trajectories (from the Skeptical Science RCP report; click for larger image):

RCP Emission Trajectories jpeg

And if you concentrate on the blue line in the CO2 chart, you can see that around 24 giga tonnes of carbon are expected to be emitted in 2060. In yesterday’s blog post I was on working in units of tonnes of CO2. In the above chart, while the subject is CO2, the y-axis is in carbon. For those who have forgotten high school chemistry, you have to remember this:

CO2 jpeg

So when we move from calculations working in tonnes of carbon to tonnes of CO2 we have to multiple by 3.67 (44 ÷12) and vice versa. Joe Romm had a great piece in Climate Progress a while ago highlighting the number of people who get caught out through mixing up CO2 and carbon units. Accordingly, the 24 giga tonnes of carbon in 2060 is equivalent to about 88 giga tonnes of CO2. To put this in perspective, what are the big emitters putting out today:

Regional Emissions to 2019 jpeg

European emissions are already in decline and US emissions are flatlining. China’s emission growth will decelerate because its fixed-investment driven GDP growth model will come to the end of its natural life. China is also just about to enter its own demographic transition, and we have all see what such a transition did to Japanese economic growth (and by extension its emissions).

Obviously, India and other developing nations will increase their emissions, but they are unlikely to be able to replicate China’s export-led growth model. Further, with every passing year, the grid parity of renewables falls. Prime Minister Modi announced a push toward renewables when meeting President Obama. This was not just as a diplomatic gesture ahead of the Paris climate talks, but also as a pragmatic measure to buttress India’s energy independence and reduce the country’s exposure to volatile fossil fuel price movements.

So the cup half full is that RCP 8.5 looks unlikely–but the cup half empty is that RCP 6.5 is pretty awful climate-wise all the same.

The New IPCC Report and Climate Change Fatigue

Six years ago, the release of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) caused a considerable stir. I suspect that the publication of the Fifth Assessment Report (AR5), with the first instalment coming this week, will be met with a yawn.

What has changed? I would cite four main factors: 1) the Great Recession, 2) the coordinated and well-financed campaign of climate scepticism, 3) the hiatus in temperature rise and, last but not least, 4) climate change fatigue. I further suspect that even if 1) through 3) had not occurred, 4) alone would have been sufficient to break the momentum of any action to mitigate climate change.

So why can’t we keep our concentration in the face of what must be the greatest threat faced by humanity in the last 10,000 years? Perhaps because the lag between cause and effect, which in the case of climate change is measured in decades rather than years, is just too big.

In the past, I believed that life insurance offered some hope as a role model for evaluating long-horizon risks since the industry is built on individuals evaluating outcomes decades into the future. But in the case of life insurance, individuals can take a rough stab at the distribution of future risk by looking at the distribution of current risk.

A twenty-something woman with young children knows that there is an outside chance that she (or her partner) could die due to a heart attack, stroke or cancer in her thirties or forties. Why? Because out of the few hundred friends and acquaintances that she has come into contact with over the years, she probably knows, either directly or indirectly, more than one person who has died young. In short, life insurance mells well with an individual’s personal life narrative.

But climate change doesn’t. The risk is abstract to the extent that it has no connection with the life experience of most people. Even the burning embers diagram of the Third Assessment Report (TAR) of 2001 does a poor job of communicating risk (and even this was excluded from AR4 for political reasons as you can read here), since it is just a representation of broad categories of risk and not based on experiences that individuals can internalise:

Burning Embers jpeg

Therefore, while the decadal unit of measurement is most appropriate for measuring the extent and effects of anthropogenic global warming (AGW), it appears too long for social and political action to coalesce. Yet AGW is moving at lightening speed when compared with natural climate change.

The climate scientist Stefan Rahmstorf, writing in the scientist-led blog Real Climate, highlights a recent paper by Marcott et al in Science that reconstructs the global temperature record back over the last 11,000 years. This period, termed the Holocene, encompasses the years since the last glacial period ended, which is broadly commensurate with the rise of human civilisation.

Marcott jpeg

As you can see, we were merrily moving in slow motion toward a new ice age when we started to burn fossil fuels. Rahmstorf then kindly provides us with a chart that adds the back story of temperature during the last ice age plus the IPCC’s central estimate of temperature out to 2100 based on the most likely fossil fuel emission trajectory. The step change is obvious, but is still not fast enough to impact on the future expectations of voters.

Global Temperature Since Ice Age jpeg

With no urge to mitigate emissions visible within the broader population, we appear to be reduced to praying a) that climate sensitivity to a CO2 will come in at the low end of estimates, and b) that this will give us sufficient time for a backstop non fossil-fuel energy technology to be developed and scaled up before extremely dangerous climate change is locked in.

This is a pure, high-stakes gamble: if we don’t get lucky with sensitivity and technology, we are left with a horrendous pay-off in terms of negative climate change effects. Unfortunately, no means of conveying this threat in a way that meshes with the life narratives of ordinary individuals appears to exist.

The Supreme Folly of Buying Oceanfront Property

If one wants to have an opinion on climate change, you need to at the very least have read the Summary for Policy Makers from the Fourth Assessment Report (AR4, 2007) of the Intergovernmental Panel on Climate Change (IPCC). Is this too much to ask? It is only 18 pages long!

Within the text, you find this chart on temperature and sea level rise (click for larger image):

IPCC Sea Level jpg

The range of seal level rise estimates across the scenarios goes from 18 cm to 59 cm. Nothing to be alarmed about? Let’s read the column text within the chart:

Model-based range excluding future rapid dynamical changes in ice flow

That basically means any ice sheet melt factors that are difficult to measure. In other words, we estimate sea level rise risk but without including the risky bits. The years flow by, and the science moves on. Here are the sea level rise scenarios from  the United States National Climate Assessment dated December 2012 (click for larger image):

Sea Level Scenarios jpg

The range is now 20cm to 200cm including all the risky bits. An oceanfront property that is economically feasible to defend with, say, 20cm of sea level rise may not be defendable at one metre plus. And note that the market is not stupid enough to wait until inundation before marking down the price. Once the market predicts the deluge decades ahead with a reasonable degree of certainty, prices are correspondingly marked down.

That absolutely prime piece of oceanfront property suddenly moves from a freehold to a leasehold valuation metric. Caveat emptor.

The Emissions Stories We Tell

In the climate change causation chain—from emissions, to greenhouse gas concentrations, to temperature change, to environmental impacts—the impacts are often the most difficult part of the chain to grasp. A major report by the UK Met Office Hadley Centre released at the beginning of December is, therefore, especially welcome, particularly as it incorporates 24 individual country studies (here) on climate impacts.

For the UK, the Met Office makes the following projection:

The UK is projected to experience temperature increases of up to around 3°C in the south and 2.5°C further north. The agreement between models is moderate in the south of the UK and low further north.

To start putting this in context, the 3C number above is by the year 2100 and is the change over the 30 year average for the 1960-1990 period (which is used as the baseline). For rainfall, we see this summary statement:

Europe shows a strong contrast in projected precipitation changes, with large decreases in the south and large increases in the north. The UK falls towards the northern region with generally increasing precipitation, with projected increases of up to 10%, though some southern parts of the UK may experience decreases of up to 5%. There is generally good agreement between ensemble members over the north of UK, but moderate agreement further south, indicating uncertainty in the position of the transition zone between increasing and decreasing precipitation over Europe.

The report then goes on to consider a number of sectors in turn: crop yields, food security, water stress and drought, pluvial flooding (rainfall saturation), fluvial flooding (river related), cyclones (extreme winds) and coastal impacts.

With such a broad spectrum of topics to choose from, a journalist covering the report has ample opportunity to push their own particular agendas. This headline from the Guardian:

Met Office warns of UK climate risks: Britain will experience water shortages and flooding by the end of the century if temperatures are left unchecked, analysis shows

And this from the Daily Mail:

Global warming would BOOST Britain’s farm crops by 10pc

While this blog occasionally focuses on the distorted press coverage of climate change, this is not a topic I want to pursue today. Overall, I am more interested in trying to understand the risks that climate change poses to individuals and their families. In this vein, not one newspaper deemed it necessary to mention the critical assumption the Met Office made: namely, the emission path underpinning their climate impact forecasts. Change this premise and you change the projection. Accordingly, the emission path used by the Met Office, which is clearly stated in the report summary, needs to be highlighted.

For the A1B emissions scenario the UK is projected to experience temperature increases of up to around 3°C in the south and 2.5°C further north.

So the projections given by the Met Office are premised on the world following the A1B emissions scenario; if the world doesn’t follow this scenario, the Met Office’s projections are invalid.

The A1B scenario came out of a report entitled the Special Report on Emissions Scenarios (SRES) published by the Intergovernmental Panel on Climate Change (IPCC) in 2000. These SRES scenarios formed the basis of the IPCC’s Third Assessment Report (TAR) published the same year and were also used for the Fourth Assessment Report (AR4) published in 2007. In reality, the scenarios are thought exercises. In the IPCC’s words:

Future greenhouse gas (GHG) emissions are the product of very complex dynamic systems, determined by driving forces such as demographic development, socio-economic development, and technological change. Their future evolution is highly uncertain. Scenarios are alternative images of how the future might unfold and are an appropriate tool with which to analyse how driving forces may influence future emission outcomes and to assess the associated uncertainties.

Indeed, the IPCC is so keen to disabuse us of the idea that the scenarios have any objective probability that they use the term ‘storylines’ (hence the title of this post):

Four different narrative storylines were developed to describe consistently the relationships between emission driving forces and their evolution and add context for the scenario quantification. Each storyline represents different demographic, social, economic, technological, and environmental developments, which may be viewed positively by some people and negatively by others.

The scenarios cover a wide range of the main demographic, economic, and technological driving forces of GHG and sulfur emissions2 and are representative of the literature. Each scenario represents a specific quantitative interpretation of one of four storylines. All the scenarios based on the same storyline constitute a scenario “family”.

If you are not familiar with the the IPCC’s scenario categories, then the ‘A’ scenarios are broadly fast growth while ‘B’ ones sacrifice some growth for environmental sustainability. Likewise the ‘1’ refers to a converging world, while ‘2’ sees lots of different developmental paths. This gives a matrix of four major families (or ‘storylines’ to use the IPCC’s wording) as depicted by the image below:

Simplistically, A1 is close to what we have seen over the last decade: the triumph of the so called Washington consensus model of rapid industrialisation, free markets and open borders; global capitalism reins supreme, and citizen-consumers realise their personal dreams through shopping at the mall. B1, by contrast, would be something like a sustainable nirvana: perhaps E.F. Schumacher’s ‘Small is Beautiful’ but with rich countries making sacrifices to lift up the living standards of poorer countries in the name of equity and fairness.

The four storylines are then further subdivided into more scenarios. Branching out from A1 are the three scenarios A1FI, A1B and A1T. The first is a fossil fuel intensive growth scenario, the second a balanced fossil fuel/renewable scenario and the last a renewables heavy scenario.

These divisions are then subdivided yet again to produce a grand total of 40 scenarios. Note that the designation HS means that all these particular scenarios share “harmonized” assumptions on global population, gross world product, and final energy. With the OS designation, such assumptions are relaxed within a particular model.

After that quick tour of the IPCC emissions scenario methodology, let’s return to the Met Office’s choice of the A1B scenario to be the basis of its climate impact analysis. Before we do, just note again that the IPCC bent over backwards not to emphasise one scenario when its report was issued back in 2000:

No judgment is offered in this Report as to the preference for any of the scenarios and they are not assigned probabilities of occurrence, neither must they be interpreted as policy recommendations.

In other words, you choose your scenario at your own peril. The report, however, does gives us some metrics to assess how particular scenarios are fairing as the years go by. The chart below shows the A1 (dash for global growth) emission scenarios. Rather counterintuitively, A1B (the balanced technology scenario) is initially a higher CO2 emitting scenario than A1FI (the fossil fuel intensive scenario). This is purely because of the particular models chosen for each scenario.

More important, the A1FI (the top dotted line) and A1B (the thick line) scenarios part company around 2020, with CO2 emission levelling off for the latter as wind, solar and such like comes on stream in mass. Looking at the predicted CO2 emission in 2050, we can see the divergence quite starkly in the table below (click for larger image).

In a similar manner, the table below (again click for larger image) shows an emerging difference between A1FI and A1B with respect to the reliance on coal and introduction of zero carbon renewables between 2020 and 2050:

So which path is more realistic? A1B or A1FI? Over the very near term, the two paths see nearly identical emissions, but it is worth just checking to see how actual emissions have been trending vis-a-vis the scenario paths projected by the IPCC back in 2000. The chart below is taken from a presentation by the Met Office’s Richard Betts at the ‘4 Degrees and Beyond‘ climate change conference held at Oxford University. If we update the chart with the advance estimate fossil fuel CO2 emission number for 2010, which is 9.1 giga tonnes of carbon, we can see that we are currently trending along the top of the IPCC’s overall band, but close to the A1B path.

Please note though that A1B in its early years is not really a  ‘balanced technology’ path as the renewables build-out has yet to take place. And, as noted before, because of some idiosyncrasies between the A1B and A1FI models, we are currently above the fossil fuel intensive A1FI path.

Against this background, fossil fuel emissions to date don’t really help us much in  deciding whether we will end up following the A1B balanced technology path or the A1FI fossil fuel intensive path.

The next question is whether we can calibrate the IPCC scenarios by using the highly detailed International Energy Agency (IEA) scenarios as presented each year in their flagship World Energy Outlook report (which I recently posted on here). The IEA has three main emission scenarios: the 450 Scenario, New Policies Scenario and Current Policies Scenario. The 450 Scenario is a thought exercise on what is needed to be done to keep the atmospheric concentration of CO2 below 450 parts per million. Unfortunately, renewable infrastructure build is not even coming close to this scenario path, so we can put it to one side.

The Current Policies Scenario is defined as follows:

WEO-2011 also presents updated projections for the Current Policies Scenario to show how the future might look on the basis of the perpetuation, without change, of the government policies and measures that had been enacted or adopted by mid-2011.

Note this includes policies that had been adopted but not executed as, for example, China’s 12th Five-Year Plan, which includes energy intensity targets.

By contrast, the New Policies Scenario includes a broader wish list of policies that countries have flagged but not necessarily done anything about:

The New Policies Scenario incorporates the broad policy commitments and plans that have been announced by countries around the world to tackle climate energy insecurity, climate change and local pollution, and other pressing energy related challenges, even where specific measures to implement these commitments have yet to be announced.

Keeping these definitions in mind, the IEA’s CO2 emissions projections under different scenarios go out as far as 2035. In that year, the IEA sees 36.4 giga tonnes (Gt) of CO2 being emitted under the New Policies Scenario and 43.3 Gt of CO2 under the Current Policies Scenario (under the 45o Scenario, emissions would be only 21.6 Gt, around a 40% fall from the 2009 level of 28.8 Gt of CO2). By contrast, the two IPCC scenarios, A1B and A1FI, have CO2 emissions moving above 40 Gt by 2020 (note to convert carbon emissions to CO2 emissions we have to multiply by 3.67), so in the early decades they are both high growth.

By 2035, the A1FI scenario is accelerating away from the A1B scenario, with emissions that year around 66 Gt of CO2 for the former against 55 Gt for the latter. The worst case IEA Current Policies Scenario has 43.3 Gt for that year.

The conclusion we can draw this far is that the selection of the A1B scenario by the Met Office for their climate impact study looks reasonable when we look out over the foreseeable time frame of 2011-2035 as covered by the IEA. However, as we go further into the future, is does become more of a ‘story’.

The IPCC sees emissions peaking under A1B at around 60 Gt somewhere around 2050, which is about double the current level of annual fossil fuel emissions. Others are less sanguine. Ross Garnaut, the well-know Australian economist published a paper (here) that suggests emission growth rates will outstrip even the IPCC’s A1FI scenario:

Accordingly, A1B could be viewed as quite conservative near term (emission overshoots unlikely) but quite aggressive long term (emission overshoots likely). In short, we would need to base our climate impact studies on a more negative emissions  scenario if we concur with Garnaut’s observations that 1) world GDP growth rates have continued to surprise on the upside and are likely to continue to do so and 2) key countries like China, India and Indonesia are being forced into an ever greater reliance on coal to meet their increasing energy needs, and will continue to do so.

At the same time, many of the trumpeted new technology hydrocarbon sources such as shale gas, shale oil and tar sands are not carbon emission friendly. They also suffer from  a particular Peak Oil community concern: we are having to use ever-larger amounts of energy to extract a given amount of energy as the easily accessible sources have become exhausted.

Personally, I think the Met Office would be wise to tell two stories based on the IEA’s Current Policies Scenario and one with the New Policies Scenario but with the latter extrapolated out for a world with high economic growth. Policy makers need an understanding of how bad things could get from a climate impacts perspective, and the use of A1B alone does not provide this. Stories are wonderful things, but they can sometimes be misleading—and ultimately dangerous—as well.

A Big Number Gets Tweaked

If I had to nominate candidates for the title of two most important numbers in the world, they would have to be 1) the atmospheric concentration of CO2 in the atmosphere (which you can find here) and 2) the climate sensitivity of the global mean temperature to a doubling of CO2.

As esoteric as this discussion may appear, both numbers rank above such economic heavy weights as inflation, GDP growth and government debt-to-GDP ratios for the life outcomes for my kids (in my humble opinion). Basically, bad things happen as CO2 jumps and temperature rises (see here, here and here).

Now there is a lot more I would like to say about atmospheric CO2 concentration, but that will have to wait for future posts. Today, I want to focus on climate sensitivity because an academic paper in the journal Science has just been released (here) that claims the numbers we have been using up to now for climate sensitivity have been too high.

But before I quote the abstract of the new paper, it is useful to restate the existing consensus from the Intergovernmental Panel on Climate Change (IPCC)’s Assessment Report 4 (AR4) published in 2007. It can easily be found on page 12 of the Summary for Policy Makers here. The key paragraph is as follows:

The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing. It is not a projection but is defined as the global average surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values. Water vapour changes represent the largest feedback affecting climate sensitivity and are now better understood than in the TAR. Cloud feedbacks remain the largest source of uncertainty.

Now we turn to the new academic paper by Schmittner et al. and—after noting that Kelvin (K) is the equivalent to Celsius (C)—we read this:

Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K as best estimate, 2 to 4.5 K as the 66% probability range, and nonzero probabilities for much higher values, the latter implying a small but significant chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K 66% probability). Assuming paleoclimatic constraints apply to the future as predicted by our model, these results imply lower probability of imminent extreme climatic change than previously thought.

Very simplistically, the paper reconstructs the temperature record of the last glacial maximum (LGM, the height of the last ice age) 20,000 years ago. Their findings suggest that the LGM was between 2 to 3 degrees Celsius cooler than the present, against current consensus estimates of around 5 degrees. The authors then matched this temperature against the green house gas concentrations of that time. In sum, for the given difference in CO2 with the present, they got less bang for the buck in terms of CO2 impact on temperature compared with what climate models currently suggest for the future.

If we believe the new findings, then the best estimate of climate sensitivity should be reduced from 3 degrees Celsius for a doubling of CO2 to 2.3 degrees—and the range has also to be narrowed. Just to put things in context, the pre-industrial concentration of CO2 was 280 parts per million and we are now at around 390 ppm, or up 40%. Now the IPCC’s AR4 also has this to say:

450 ppm CO2-eq corresponds to best estimate of 2.1°C temperature rise above pre-industrial global average, and “very likely above” 1°C rise, and “likely in the range” of 1.4–3.1°C rise.

Now I’ve highlighted it before in another post, but I will highlight it again in this post, CO2 and CO2 equivalent are different concepts. However, at the current time, non-C02 atmospheric forcing effects currently cancel out (for a more detailed discussion of this, see here), so we are in the happy position of being able to capture what is happening by looking at the CO2 number alone—for the time being.

Moving on, we should note that the international community has decided that 2 degrees Celsius of warming marks the point as where we will experience ‘dangerous’ climate change. This is in the opening paragraph of the Copenhagen Accord:

We underline that climate change is one of the greatest challenges of our time. We emphasise our strong political will to urgently combat climate change in accordance with the principle of common but differentiated responsibilities and respective capabilities. To achieve the ultimate objective of the Convention to stabilize greenhouse gas concentration in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system, we shall, recognizing the scientific view that the increase in global temperature should be below 2 degrees Celsius, on the basis of equity and in the context of sustainable development, enhance our long-term cooperative action to combat climate change.

To recap, we have a best estimate of climate sensitivity of 3 degrees. And based on this number,  atmospheric CO2-equivalent should be capped at 450 ppm to hold temperature rise to around 2 degrees. This, in turn, is because 2 degrees of warming is deemed the level at which ‘dangerous’ climate change develops.

Now what happens if the 3 degree number is incorrect and should be 2.3 degrees? Well, the first reaction is to think that the 450 ppm ‘line in the sand’ for dangerous climate change goes out the window. Further, if this CO2 concentration number goes out the window, so do all the numbers for ‘extremely dangerous’ climate change, and for that matter ‘catastrophic’ climate change. If so, the carbon emissions paths associated with different levels of warming as talked about in my post here also have to be radically revised (click for larger image below, see here for the original article).

And, addition, the deadline for the cessation of fossil fuel based energy production plant installation calculated by the International Energy Agency (IEA) and as talked about in my last post here would also have to be reworked.

However, some caution is in order. First, this is only one paper amongst many that have tackled the question of climate sensitivity from a variety of angles; it should be judged within the context of the total body of work. Further, as with all good science, its assumptions will come under intense scrutiny to check if the methodology is correct. Unlike the climate skeptic blog comnentary, the authors of the report fully admit the tentative nature of their findings:

“There are many hypotheses for what’s going on here.  There could be something wrong with the land data, or the ocean data.  There could be something wrong with the climate model’s simulation of land temperatures, or ocean temperatures.  The magnitudes of the temperatures could be biased in some way.  Or, more subtly, they could be unbiased, on average, but the model and observations could disagree on the cold and warm spots are, as I alluded to earlier.  Or something even more complicated could be going on.

Until the above questions are resolved, it’s premature to conclude that we have disproven high climate sensitivities, just because our statistical analysis assigns them low probabilities.”

The excellent site Skeptical Science has a great post on the Schmittner et al. paper here.  After going through the technical challenges in considerable depth, they also note a critical, and inconvenient truth, if the article’s findings are correct:

In short, if Schmittner et al. are correct and such a small temperature change can cause such a drastic climate change, then we may be in for a rude awakening in the very near future, because their smaller glacial-interglacial difference would imply a quicker climate response a global temperature change, as illustrated in Figure 4.

As Figure 4 illustrates, although the Schmittner et al. best estimate for climate sensitivity results in approximately 20% less warming than the IPCC best estimate, we also achieve their estimated temperature change between glacial and interglacial periods (the dashed lines) much sooner.  The dashed lines represent the temperature changes between glacial and interglacial periods in the Schmittner (blue) and IPCC (red) analyses.  If Schmittner et al. are correct, we are on pace to cause a temperature change of the magnitude of an glacial-interglacial transition – and thus likely similarly dramatic climate changes – within approximately the next century.*

In the run-up to the publication of the IPCC’s AR5 report in 2013, it will be critical to see if a new consensus number emerges that is different from that of the last AR4 report in 1997—a consensus that takes all the new findings made over the last few years into consideration. As this number changes, so will the world.

Odds of Cooking the Kids: Part 1

Apologies for the large gap since my last post; the result of me relocating from one country to another.

A recurring theme of this blog is how to assess the risk of climate change to one’s family. Stuart Staniford over at Early Warning once characterised this as the  ‘Odds of Cooking the Grandkids’. As such, his post plugs into the central theme of this blog: the badness of the potential outcomes (the cooking of the grandkids) and the fact it should be viewed in terms of probability (the odds).

To cook the grandkids you basically need to see around 6 degrees Celsius of warming. But focussing on the grandkids is putting the cart before the horse. Before we get to the stage where we cook the grandkids, we need to parboil our own kids. And the cooking process will begin when we get above 2 degrees of warming (see here) and get progressively worse at 3 to 4 degrees (here).

To extend the analogy, in the kitchen you have two main variables: 1) the intensity 0f the heat and 2) the duration for which the heat is applied. In climate change you have two principal variables as well: 1) the sensitivity of temperature change to an increase in atmospheric CO2 and 2) the amount of CO2 we pump into the atmosphere. If you are able to understand these two variables—and follow them as they evolve through time—then you will get a better idea of the odds of cooking the kids. Continue reading