Tag Archives: Skeptical Science

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.

Permafrost, Chimpanzees, the Savanna and Risk

In my  weekend links, I highlighted a new study published in Science. It is behind a pay wall, but has been well covered by Climate Central and Climate Progress. The study provides us with a good excuse to revisit the whole topic of climate risk.

The paper in question is an empirical study of past permafrost thaw at different temperatures. To summarise the conclusion, stalactite and stalagmite growth in Siberian caves suggests that significant permafrost thaw took place 400,000 years ago when the global mean temperature was around 1.5 degrees Celsius higher than it is today. This level of specificity is new, and is important for not being model based. Incidentally, we have an accurate temperature record going back around 800,000 years through the study of ice cores.

When such studies come through, I think it always useful to place them within a risk component analysis framework. As a reminder, risk is best defined as probability times effect—or  more specifically probability times net harmful effect. It is also worth recalling that we should not get sidetracked by the accusation that such studies lack certainty. The human condition is one of decision-making under uncertainty. As individuals, the only real certainty we have in our lives is death.

Keeping these points in mind, climate change can be viewed as a chain of risk components, each of which has its own probability distribution. We move from emissions, through atmospheric concentrations (the study of the airborne fraction that I blogged about here), to climate sensitivity, until finally we arrive at the net harmful effects on both individuals and societies.

Continue reading

The Irony of ‘Alarmists’ Who Err on the Side of Least Drama

Try searching the headlines of Anthony Watts’ WUWT blog for the words “alarmist” or “alarmism” over the past year and you will get 17 hits. The words are never clearly defined but imply that climate scientist claims are exaggerated and thus unworthy of merit.

Fortunately, a literature review by Brysse et al has recently been released that looks into whether this is true (the original is here and Skeptical Science also provides a good summary here).

Restated, the question is whether the scientific community, for which the Intergovernmental Panel on Climate Change (IPCC) can be used as a proxy, has made exaggerated predictions. For a full answer to this question, please read the original article or the Skeptical Science post. In summary, the article’s conclusion is that the IPCC has been too cautious in its predictions with respect to sea level rise, Arctic sea ice extent retreat, snow cover reduction, the rise in carbon emissions and ice sheet melt. Hurricane intensity and global mean temperature rise have been in line with predictions.

The most interesting part of the article deals with why scientists have had a tendency to be conservative in their predictions—what the study calls to ‘err on the side of least drama (ESLD)’. In their words: Continue reading

Risk, Sensitivity and Sifting the Studies

Global warming? How bad could it get? Of course, with all of us being knowledgable about risk, we understand that this is really a question of probability multiplied by effect (that, in turn, means probable-but-quite-bad stuff happening all the way through to possible-but-bloody-awful stuff happening).

But lets chunk that up into three manageable variables: 1) how much CO2 we are throwing up into the atmosphere, 2) how much warming that CO2 is creating, and 3) how much damage the warming is causing.

This gives anyone of a “skeptical” disposition  three lines of attack: 1) dispute the trajectory of fossil fuel emissions, 2) uncover academic papers that suggest a low climate temperature sensitivity to CO2 or 3) welcome the warmer world as being beneficial to mankind.

Out of the primeval swamp that is the blogosphere, a Darwinian struggle has led to two sites emerging triumphant (one on either side of the Atlantic) as the alpha male climate “skeptic” clearing houses. From the U.S., we have Watts Up With That, and from the U.K. Bishop’s Hill. If you read any article bashing climate change, it is a good bet that the columnist or journalist sourced it from one of these two.

Not surprising, therefore, that both blogs have jumped on an as-yet-unpublished study by Norwegian researchers stating that climate sensitivity to a doubling of CO2 is as low as 1.9 °C (see here and here).

As a non-scientist but a student of risk, I suggest a three-step approach to any claim that here is little or no risk from climate change, and I use the Norwegian study as an example of this process. Continue reading

Trends, Fluctuations and Having Skin in the Game

Anyone who has seriously invested in financial markets starts by learning to separate fluctuations from the trend. If you don’t, your life in the markets will be nasty, brutish and short. The same applies to any analysis of global temperature. You have a trend, principally driven by greenhouse gas concentrations in the atmosphere; and you have fluctuations, principally driven by the El Nino Southern Oscillation (ENSO) cycle.

When we are in the  El Niño phase, Pacific ocean temperatures are higher then average; in a La Niña phase, lower. The impact is significant enough to influence overall global mean temperature. Accordingly, if you wish to make a statement about the recent trend in global warming, start by adjusting for the ENSO fluctuation. Of course, many don’t. Indeed, the claim that global warming has ceased over the last decade is frequently aired in many a newspaper column (like this from the Wall Street Journal), not just the wackier end of the blogosphere.

Let us for a minute look at the distribution of El Niño and La Niña events over the last couple of decades. The excellent blog Skeptical Science does just that (here) and presents the following chart (click for larger image):

Temperature and ENSO jpg

The piece concludes with the following: Continue reading

Climate Change, Boiling Frogs and Pearl Harbors

As we move further into 2012, media interest in climate change continues to decline. The chart below from  The Center for Science and Technology Research at the University of Colorado-Boulder shows a clear downward trend for world newspaper coverage. At the national level, a similar time series for US newspaper coverage can be found here and the UK here.

In my mind, media coverage of climate change is probably determined by four factors: 1) the setting of new temperature records, 2) visible iconic climate events, 3) media coverage of scientific studies that contain pessimistic forecasts of future climate and 4) extreme weather. Continue reading