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IPCC AR5: Climate Extremes

by Bjinse Fri Oct 4th, 2013 at 05:23:43 AM EST

The IPCC released its first of three assessment reports on climate change, available for download here. The report, still without a slick format, provides an opportunity to compare findings and scenario's in regard to its most recent counterpart, released in 2007, available for download here.

I will compare both reports of Working Group 1 on a number of climate topics that have drawn my interests over the years. With over 2200 pages, the new report is staggeringly huge, more than twice as thick as its predecessor, and the number of covered topics is vast. I start with comparing the reports on climate extremes.


In contrast with AR4, a larger range of climate extremes (and assessment on the indices which define such climate extreme) have been dedicated to a separate section. This is also visible in the Technical Summary in the AR5, where progress on understanding of climate extremes is now summarized.

Temperature & Precipitation Extremes

On temperature and precipitation extremes, the AR4 and AR5 largely concur. AR4 found that temperature extremes (hotter days and nights) had likely increased at a global scale; AR5 notches up this likelihood even further:


[N]ew analyses continue to support the AR4 and SREX conclusions that since about 1950 it is very likely that the numbers of cold days and nights have decreased and the numbers of warm days and nights have increased overall on the global scale, i.e., for land areas with sufficient data.

For precipitation extremes the AR5 writes:


It is likely that since about 1950 the number of heavy precipitation events over land has increased in more regions than it has decreased. Regional trends vary but confidence is highest for central North America with very likely trends towards heavier precipitation events.

Heat waves

On heatwaves, AR4, chapter 3, did not elaborate specifically on heatwaves, although it summarized in Table 3.8 that on a global scale heatwaves had likely increased since the middle of the 20th century. (Likely: over 66 percent probability.)

On this topic, AR5, chapter 2, reads:

There is only medium confidence that the length and frequency of warm spells, including heat waves, has increased since the middle of the 20th century mostly due to lack of data or studies in Africa and South America. However, it is likely that heatwave frequency has increased during this period in large parts of Europe, Asia and Australia.

This marks a first deviation with respect to AR4: for regions with sufficient data, science indicates increased numbers of heatwaves since 1950. An assessment on the global scale can not yet be made, but only because of a paucity in data or studies for the remaining regions.

Droughts

Similar to heatwaves, AR4 tallied increasing droughts in several regions but lacked a perspective on global scale, although it did note:

While there are numerous indices and metrics of drought, many studies use monthly precipitation totals and temperature averages combined into a measure called the Palmer Drought Severity Index (PDSI). The PDSI calculated from the middle of the 20th century shows a large drying trend over many Northern Hemisphere land areas since the mid-1950s, with widespread drying over much of southern Eurasia, northern Africa, Canada and Alaska (FAQ 3.2, Figure 1), and an opposite trend in eastern North and South America. In the Southern Hemisphere, land surfaces were wet in the 1970s and relatively dry in the 1960s and 1990s, and there was a drying trend from 1974 to 1998. Longer-duration records for Europe for the whole of the 20th century indicate few significant trends. Decreases in precipitation over land since the 1950s are the likely main cause for the drying trends, although large surface warming during the last two to three decades has also likely contributed to the drying. One study shows that very dry land areas across the globe (defined as areas with a PDSI of
less than -3.0) have more than doubled in extent since the 1970s, associated with an initial precipitation decrease over land related to the El Niño-Southern Oscillation and with subsequent increases primarily due to surface warming.

AR5, TS 4.7, p38:


While the AR4 concluded that it is more likely than not that anthropogenic influence has contributed to an increased risk of drought in the second half of the 20th century, an updated assessment of the observational evidence indicates that the AR4 conclusions regarding global increasing trends in hydrological droughts since the 1970s are no longer supported. Owing to the low confidence in observed large-scale trends in dryness combined with difficulties in distinguishing decadal-scale variability in drought from long-term climate change, there is now low confidence in the attribution of changes in drought over global land since the mid-20th century to human influence.

Floods

In 2007, the first report of the AR4 did not include a scientific assessment on the frequency or magnitude of floods, in fact, it sparsely mentioned floods, although European floods in Germany were briefly listed as an example. In Chapter 9, on attribution, it was observed, though not referenced:


Climate models predict that human influences will cause an increase in many types of extreme events, including extreme rainfall. There is already evidence that, in recent decades, extreme rainfall has increased in some regions, leading to an increase in flooding.

AR5 has a separate section on floods in chapter 2, where it concludes:


While the most evident flood trends appear to be in northern high latitudes, where observed warming trends have been largest, in some regions no evidence of a trend in extreme flooding has been found, e.g., over Russia based on daily river discharge (Shiklomanov et al., 2007). Other studies for Europe (Hannaford and Marsh, 2008; Renard et al., 2008; Petrow and Merz, 2009; Stahl et al., 2010) and Asia (Jiang et al., 2008; Delgado et al., 2010) show evidence
for upward, downward or no trend in the magnitude and frequency of floods, so that there is currently no clear and widespread evidence for observed changes in flooding except for the earlier spring flow in snow dominated regions (Seneviratne et al., 2012).


In summary, there continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.


(Source: NASA)

Tropical Cyclones

The AR4 contained a large section on tropical cyclones, or hurricanes, and on studies for the different ocean basins. For an analysis on the global scale, it read:


Globally, estimates of the potential destructiveness of hurricanes show a substantial upward
trend since the mid-1970s, with a trend towards longer storm duration and greater storm intensity, and the activity is strongly correlated with tropical sea surface temperature. These relationships have been reinforced by findings of a large increase in numbers and proportion of strong hurricanes globally since 1970 even as total numbers of cyclones and cyclone days decreased slightly in most basins. Specifically, the number of category 4 and 5 hurricanes increased by about 75% since 1970. The largest increases were in the North Pacific, Indian and Southwest Pacific Oceans. However, numbers of hurricanes in the North Atlantic have also been above normal in 9 of the last 11 years, culminating in the record-breaking 2005 season.

As detailed previously on ET, most of these conclusions were overturned in 2010 as the hurricane science community moved together to hammer out its differences and the findings of these papers were underlined once more in the assessment of the SREX report. The AR5 concludes:


Current datasets indicate no significant observed trends in global tropical cyclone frequency over the past century and it remains uncertain whether any reported long-term increases in tropical cyclone frequency are robust, after accounting for past changes in observing capabilities (Knutson et al., 2010).

...

However over the satellite era, increases in the intensity of the strongest storms in the Atlantic appear robust (Kossin et al., 2007; Elsner et al., 2008) but there is limited evidence for other regions and the globe.

...

In summary, this assessment does not revise the SREX conclusion of low confidence that any reported longterm (centennial) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities. More recent assessments indicate that it is unlikely that annual numbers of tropical storms, hurricanes and major hurricanes counts have increased over the past 100 years in the North Atlantic basin. Evidence however is for a virtually certain increase in the frequency and intensity of the strongest tropical cyclones since the 1970s in that region.

Abrupt Climate Change - Catastrophes

Chapter 12 in the AR5 summarizes the scientific understanding on a range of climate doom scenario's, from catastrophic methane release to Greenland ice collapse to the shutdown of the 'Gulf Stream', all sensational scenario's which logically attract media attention, Hollywood script writers and even contributors at European Tribune.

In AR4, analysis on abrupt climate change events was scattered throughout the report, and varying degrees of likelihood for these events were expressed. With AR5, the definition of abrupt climate change has been modified:


Synthesis and Assessment Product 3.4 of the U.S. Climate Change Science Program CCSP (CCSP, 2008b). We define abrupt climate change as a large-scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems (see
Glossary). Other definitions of abrupt climate change exist. For example, in the AR4 climate change was defined as abrupt if it occurred faster than the typical time scale of the responsible forcing.

AR5 Table 12.4 summarizes the scientific consensus of a range of abrupt climate change scenarios with one swift stroke, which speaks for itself:


Table 12.4

To summarize. With the AR5, scientific consensus on climate extremes is portrayed more focussed and with richer detail in comparison to AR4. The new IPCC report relies heavily on findings of its special report on extreme events (SREX), published early 2012. Given that the assessment in SREX upset or overturned conclusions of the AR4 on some of the more dramatic climate extremes, it should not be surprising that also AR5 differs with AR4 in several respects.

In line with IPCC's previous reports, the AR5 finds a discernable increasing trend for temperature extremes and extreme precipitation events at the global scale and increasing frequency of heat waves at regional scales since the 1950s. In contrast with findings in AR4, no trend is discerned for droughts, floods, or tropical storms at the global scale.

Furthermore, globally catastrophic doom scenario's such as the abrupt shutdown of the Atlantic thermohaline circulation, dramatic ice sheet collapse or methane release (either from permafrost or oceanic clathrates) are presently considered unlikely. With the exception of the scenario for disappearing Arctic summer ice, other abrupt scenario's have no scientific agreement or evidence, that is, no decisive answer.

With the scientific consensus as captured in the AR5 report, the IPCC puts to rest general yet popular claims that climate change already results in increasing floods, droughts or hurricanes, and invalidates claims that climate change already risks the above listed catastrophic scenario's, as such claims are both scientifically unsupportable and outside the scientific consensus.

Finally, one could observe that the IPCC has commendably increased attention for analysing climate extremes at the regional level, and most likely the second report (to be released next year) will further elaborate on vulnerabilities at that scale.

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Personally, it's heartening to see how much care and dedication has been put by the IPCC to resolve these returning issues, which were prone to controversy. This is science at its best. With the AR5 the scientific ground for alarmism has noticeably shrunk - although there's plenty left for political activists on other topics.

I'm open to suggestions that I should start worrying more about economic collapse.

by Bjinse on Fri Oct 4th, 2013 at 05:36:41 AM EST


In the Neurozone, there can be only one.
by Migeru (migeru at eurotrib dot com) on Fri Oct 4th, 2013 at 06:58:36 AM EST
[ Parent ]
* cough cough *

DoDo:

Let me make a bet: in the next IPCC assessment this year or next, I bet that (1) the assessment of climate change influence on flood risk will be less inconclusive, (2) it will reference the studies mentioned in this thread.

by Bjinse on Fri Oct 4th, 2013 at 05:44:16 AM EST
With the scientific consensus as captured in the AR5 report, the IPCC puts to rest general yet popular claims that climate change already results in increasing floods, droughts or hurricanes at a global level

FIFY... sorry to deflate your strawman, but the absence of conclusive evidence of overall global trends in increased drought, flooding etc. in no way invalidates the evidence of regional increases of such stuff (which is what is discussed in the article you linked).

This is so basic an "error" that I'm obliged to conclude that you are looking for a fight...

And I guess we'll have to await the forthcoming regional analysis before we can see the debate with Dodo.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Fri Oct 4th, 2013 at 07:31:52 AM EST

Droughts:


SREX (Seneviratne et al., 2012) assessed that there was medium confidence that anthropogenic influence has contributed to some changes in the drought patterns observed in the second half of the 20th century based on attributed impact of anthropogenic forcing on precipitation and temperature changes, and that there was low confidence in the assessment of changes in drought at the level of single regions.

...

There is not enough evidence to support medium or high confidence of attribution of increasing trends to anthropogenic forcings as a result of observational uncertainties and variable results from region to region (Section 2.6.2.2). Combined with difficulties described above in distinguishing decadal scale variability in drought from long-term climate change we conclude consistent with SREX that there is low confidence in detection and attribution of changes in drought over global land areas since the mid-20th century.

Tropical cyclones:


There is low confidence in basin-scale projections of changes in intensity and frequency of tropical cyclones in all basins to the mid-21st century

On floods, the AR5 confirms the conclusions of the SREX report, which concluded:

there is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at a regional scale because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of 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.
by Bjinse on Fri Oct 4th, 2013 at 12:09:24 PM EST
[ Parent ]
The above quote on tropical cyclones taken from AR5 was on projections. However, there is no divergence on regional or global analysis on tropical cyclones:


There is low confidence in long-term (centennial) changes in tropical cyclone activity, after accounting for past changes in observing capabilities.


Current datasets indicate no significant
observed trends in global tropical cyclone frequency over the past century and it remains uncertain whether any reported long-term increases in tropical cyclone frequency are robust, after accounting for past changes in observing capabilities (Knutson et al., 2010).
by Bjinse on Fri Oct 4th, 2013 at 01:56:07 PM EST
[ Parent ]
You underline, for cyclones, the question of frequency, while sidestepping the stated clear evidence on intensity :
However over the satellite era, increases in the intensity of the strongest storms in the Atlantic appear robust (Kossin et al., 2007; Elsner et al., 2008) but there is limited evidence for other regions and the globe.

 (Obviously, there is a time lag: AR5 cannot take into account the devastating cyclones hitting Asia in the last couple of years. It would be surprising if a trend were not noted in the next round.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II
by eurogreen on Sun Oct 6th, 2013 at 07:16:33 AM EST
[ Parent ]
My diary noted the observed intensity in hurricanes for the Atlantic basin since 1970s, so I fail to see where I would 'sidestep'.

Considering the subject of hurricane intensity, the following remark from the AR5 should suffice:

Time series of cyclone indices such as power dissipation, an aggregate compound of tropical cyclone frequency, duration, and intensity that measures total wind energy by tropical cyclones, show upward trends in the North Atlantic and weaker upward trends in the western North Pacific since the late 1970s (Emanuel, 2007), but interpretation of longer-term trends is again constrained by data quality
concerns (Landsea et al., 2011).

...

In summary, this assessment does not revise the SREX conclusion of low confidence that any reported longterm (centennial) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities.

SREX's conclusion :


Based on research subsequent to the AR4 and Kunkel et al. (2008), which further elucidated the scope of uncertainties in the historical tropical cyclone data, the most recent assessment by the World Meteorological Organization (WMO) Expert Team on Climate Change Impacts on Tropical Cyclones (Knutson et al., 2010) concluded that it remains uncertain whether past changes in any tropical cyclone activity (frequency, intensity, rainfall) exceed the variability expected through natural causes, after accounting for changes over time in observing capabilities. The present assessment regarding observed trends in tropical cyclone activity is essentially identical to the WMO assessment (Knutson et al., 2010): there is low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities.

I'm well aware that projections possibly suggest an increase of the number of the strongest hurricanes for some basins - but there is no strong consensus on this either (see chapter 14 of the AR5 or SREX).

by Bjinse on Sun Oct 6th, 2013 at 09:10:58 AM EST
[ Parent ]
I wish I could conclude, as you apparently do, that the AR5 allows us to stop worrying about the climate...

You acknowledge the climate disruptions (changes in precipitation, rising temperatures etc, you seem unconcerned about sea level...) but you conclude that these are not a major worry, because lack of data and confounding factors don't yet point to clear causality to catastrophic weather events.

I'm happy for you, I guess.

I'm being hit repeatedly over the head with a sledgehammer, but it's OK, because the medical tests don't give conclusive proof of brain damage yet.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Sun Oct 6th, 2013 at 07:15:53 AM EST
[ Parent ]
as you apparently do, that the AR5 allows us to stop worrying about the climate...

you seem unconcerned about sea level...)

you conclude that these are not a major worry, because lack of data and confounding factors don't yet point to clear causality to catastrophic weather events.

All false.

I suggest, again, that you contest me on what I write, not on what you think I 'apparently' write.

by Bjinse on Sun Oct 6th, 2013 at 09:33:27 AM EST
[ Parent ]
With the AR5 the scientific ground for alarmism has noticeably shrunk - although there's plenty left for political activists on other topics.

I'm open to suggestions that I should start worrying more about economic collapse.

So you seem to find that the AR5 gives you reason to worry less about climate change.
(Or where you being ironic?)

For example : you seem to be equating absence of evidence (or inconclusive evidence) with evidence of absence. Because there is not a clear worldwide trend to increased drought, or increased flooding, you conclude we should worry less.

But I wonder why you think the absence of clearly measurable worldwide trends demonstrates anything at all : this smells like a strawman. I don't know anyone who has claimed that "global warming will cause worldwide drought", or "global warming will cause worldwide flooding". On the contrary, global warning is expected to cause disruptive climate change in every region.  Intuitively, I would expect that overall warming would increase both floods and drought; but I wouldn't be surprised if, for example, increased flooding in certain regions coincided with decreases in other regions. And I expect that various regions are experiencing disruptive climate change which is currently poorly measured, or which is measured but lacks a history of measurements to detect trends.

As we have previously discussed with respect to flooding, various confounders such as land use changes make trends difficult to prove, even in areas where relatively good records exist. These also tend to be the wealthier regions, which are better at mitigating the effects anyway. As an anecdotal example : a decade-long drought in Texas hardly causes a blip in economic output; a third world nation which experienced something similar might experience collapse of subsistence food production, mass starvation and failure of institutions.

So, I will certainly be interested in discussing the regional analyses when they are released. Perhaps they will trouble your Panglossian calm.

On the other hand, I have no objection to you worrying more about economic collapse (one can never worry too much!)

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Sun Oct 6th, 2013 at 02:02:53 PM EST
[ Parent ]
So you seem to find that the AR5 gives you reason to worry less about climate change.

you seem to be equating absence of evidence (or inconclusive evidence) with evidence of absence.

Still false.

I observe that 'the scientific ground for alarmism has noticeably shrunk' for climate extremes and abrupt climate scenario's, which I think the IPCC reports demonstrate. If this reading is incorrect, then I welcome to hear about that.

I appreciate your passion on this subject, and your attention for detail, which also affects my writing, turning more and more science orientated, and thus more emotionally detached.

I live in the Netherlands. If I were 'Panglossian calm' (nice!) about climate change, of course I would not be writing about it.

by Bjinse on Mon Oct 7th, 2013 at 06:04:33 AM EST
[ Parent ]
It got down to -4 C (25 F) in Colorado Springs last night, which is a new record. Therefore, climate change is proven.
by asdf on Sat Oct 5th, 2013 at 12:33:56 PM EST


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