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Precipitation - steady as she goes

A new paper by van Wijngaarden and Syed in the Journal of Hydrology notes a claim by the IPCC:

...the IPCC has reported that precipitation increased in some regions by as much as 1% in each decade of the 20th century.

The paper's authors then set about testing this claim.

The percentage annual precipitation change relative to 1961–90 was plotted for 6 continents; as well as for stations at different latitudes and those experiencing low, moderate and high annual precipitation totals. The trends for precipitation change together with their 95% confidence intervals were found for various periods of time. Most trends exhibited no clear precipitation change. The global changes in precipitation over the Earth’s land mass excluding Antarctica relative to 1961–90 were estimated to be: 1.2 ± 1.7, 2.6 ± 2.5 and 5.4 ± 8.1% per century for the periods 1850–2000, 1900–2000 and 1950–2000, respectively. A change of 1% per century corresponds to a precipitation change of 0.09 mm/year.

So if my maths is correct, the IPCC is out by as much as an order of magnitude. Perhaps the regions they were testing were smaller.

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Reader Comments (14)

Bishop - the actually abstract says - "relative to 1961–90 were estimated to be: −1.2 ± 1.7, 2.6 ± 2.5 and −5.4 ± 8.1% per century for the periods 1850–2000, 1900–2000 and 1950–2000, respectively".
So over the century there was a 2,6% increase (+/-2,5!), but for the other two stretches the sign is negative, being most negative for 1950-2000, though admittedly with vast error limits! So, you're right in spirit, but for the IPCC chosen period, wrong.

Dec 4, 2015 at 9:38 PM | Unregistered Commentermothcatcher

Apologies - should have read your intro more carefully! You do say '1% PER DECADE' so that's 4 x what this study reports. Also noted the biggest negative attaches to the period most associated withCO2 increase. But with those error limits, its meaningless anyway. Congratulations to the authors for publishing a negative result..

Dec 4, 2015 at 9:53 PM | Unregistered Commentermothcatcher


am I to understand that global precipitation is statistically unchanged since 1850? I thought increased precipitation was the cornerstone of Dame Julia Slingo's 'warming world'. As temperatures go up due to CO2, more water vapour goes into the atmosphere leading to increased precipitation.

The corollary of the statistical evidence is that there has been no change in the global temperature since 1850. So much for the surface temperature record.

Dec 4, 2015 at 11:02 PM | Unregistered CommenterBilly Liar

ATTP won't like this....

Dec 4, 2015 at 11:23 PM | Unregistered CommenterDavid Smith

How come are we less certain about the change `between the short period 1950 to 2000 (error +/- 8.1%) than we are for the longer period 1850 to 2000 (error +/- 1.7%)?

Aren't our record keeping standards and measurement equipment better in the period 1950 to 2000, than they were in the 19th and early 20th century?,

It was less than a decade ago that Global Warming/Climate Change was reeled out as the standard excuse for water shortages/hose pipe bans etc. This never made sense to me since the data showed little if any change in UK rainfall and to the extent that there was a trend, it showed a slight increase (not statistically significant).

Of course the real reason why this was rolled out as the standard excuse was because of poor water management and the fact that not a single new reservoir had been built in the South East in the past 25 years notwithstanding the vast rise in population and consequent demand for water. it was used as an excuse to hide management failings.

Then of course, we got the spate of flooding. Global Warming/Climate Change is now rolled out as the standard excuse for this. Once again, it is being used to cover up poor management. Poor town planning in allowing building on flood plains, and poor river management and lack of dredging etc.

The BBC and MSM never wish to look at the underlying data which would expose these claims as hocus and which would quickly identify the real problem poor lefty/liberal state management, and a failure to properly deal with an increasing population brought about by migration/immigration..

Dec 5, 2015 at 4:27 AM | Unregistered Commenterrichard verney

A new (cherry picked) paper, a new nail in the denier coffin. Surrender to the evidence, climate heathens.

Dec 5, 2015 at 8:35 AM | Unregistered CommenterAila

Why does Aila remind me of Jack Hawkins' character in Zulu?

Dec 5, 2015 at 10:46 AM | Unregistered CommenterMike Post

Why does Aila remind me of Jack Hawkins' character in Zulu?
It may have something to do with the contents of the bottle never far from his hand by the sound of it.
I suspect that the cherry-picking was done by the authors of the relevant IPCC chapters (it does, after all, say "some regions") to bolster their cash flow. But those error bars! If I applied those to Newcastle United's recent results I could have them challenging for the Premier League title!

Dec 5, 2015 at 10:59 AM | Registered CommenterMike Jackson

In the old Met Office building in Bracknell, there was a lounge area serving alcoholic beverages called the "Iso Bar".

Does the new Met Office HQ in Exeter have an "Error Bar", where the boundaries of scientific fact and fiction can be blurred, and inhibitions relaxed?

Dec 5, 2015 at 11:39 AM | Unregistered Commentergolf charlie

Aila tries to drive in nails with a hand picked cherry.

Dec 5, 2015 at 11:45 AM | Unregistered Commentergolf charlie

Golf Charlie

The Barnowl is quite close to the Met Office on Honiton Road. Not sure if that's the local.

Doesn't quite have the same ring sadly.

Exeter does have the House That Moved though.

Dec 5, 2015 at 11:58 AM | Unregistered CommenterMicky H Corbett

A small increase in precipitation with GMST wouldn't actually be good news so far as climate sensitivity goes. A large increase in precipitation with temperature implies that the atmosphere has been able to get rid of the associated increase in latent heat of condensation by radiating it to space, implying a low climate sensitivity. And vice versa.

However, this result actually suggests that precitipation increase quite strongly with temperature. A 5.4%/century incease over 1950-2010, over which period the GMST trend was 1.1 K/century per HadCRUT4, implies that precipitation has increased by ~5%/K. That is about 2.5x as fast as in GCM simulations (e.g., Stephens and Yu, ERL 5 (2010) 025209). That implies the GCMs have substantially too high a climate sensitivity.

Dec 5, 2015 at 4:43 PM | Unregistered CommenterNic Lewis

Bish: When you combine these two vague statements, you do not get a contradiction. That is because neither says anything particularly definitive.

Paper: The 95% ci for GLOBAL change in this paper is 0.01% to 0.51% per decade for 1900-2000 and -0.54% to 1.35% per decade for 1950-2000.

IPCC: "precipitation increased IN SOME REGIONS by as much as 1% IN EACH DECADE of the 20th century."

There is nothing global in the IPCC's statement. It doesn't even clearly state that the 1% increase occurred in the same place in every decade. Australia might be up 1% in the 1940s and 1980s (and may have fallen between). Equatorial Africa and East Asia could have been up 1% in the 1910s, 1970s and 1990s.

If the regions of greatest increase were twice he global average increase, then the global average increase would be 0.5% per decade, just on the edge of the confidence interval. If the regions of greatest increase were quadruple, the global average increase, then the global average increase would be 0.25% per decade, in the center of the confidence interval.

So the statements could be consistent. Or, you could be right and there could be an order of magnitude difference. For that matter, 0.01% permits two orders of magnitude difference. And -0.54% encompasses a change in the opposite direction.

Dec 6, 2015 at 11:15 PM | Unregistered CommenterFrank

Nic wrote: A small increase in precipitation with GMST wouldn't actually be good news so far as climate sensitivity goes.

Let's consider this in more mathematical terms. If the planet has an ECS of 3 K for doubled CO2, then there must be 1.2 W/m2/K increase in net outgoing radiation (OLR+reflected SWR) associated with surface warming. If evaporation rises proportionally to saturation vapor pressure, there will be a 6-7%/K increase in latent heat transfer with surface warming or about 5.2 W/m2/K. The increase in surface OLR is 5.4 W/m2/K and the increase in DLR received by the surface should be 4.8 W/m2/K (based on a blackbody model for a source (about 2 km above the surface) for DLR at 277 K emitting 333 W/m2). So we have a surface flux change of about +6 W/m2/K and a TOA flux change of 1.2 W/m2/K. This situation obviously can't persist indefinitely. I see two solutions to this dilemma:

1) Clouds reflect 4.8 W/m2/K less radiation to space. That is a large -1.4%/K change in planetary albedo that might be detectable. If a similar change in cloud cover occurred in temperate zones for a 14 K difference between summer and winter, that would mean a winter albedo of 40% and a summer albedo of 20%. For a 7 degK difference, 35% winter and 25% summer. No change of this magnitude is observed from space during the 3.5 K seasonal cycle.

2) The increase in evaporation expected from the C-C eqn is suppressed. The rate of evaporation is proportional to wind speed and the "undersaturation" of the air near the surface of the ocean. Since relative humidity is about 80% over the oceans, a 1% increase in relative humidity (predicted by AOGCMs) is a 5% decrease in "undersaturation" and evaporation. This is enough to reduce the surface flux so that it equals the TOA flux. An increase in relative humidity or a decrease in wind speed, will cause precipitation to increase less than 6-7%/K.

Unlike the papers mentioned in this post, the combination of satellite and rain gauge data from 1987-2006 reported by Wentz (2007) provides a usefully-constrained increase in precipitation over the past two decades: 1.4+/-0.5%/decade (95% ci). Warming over the same period was 0.19+/-0.04 K/decade, giving a central estimate of 7.3%/K with a 95% ci about half of this value. According to this paper, evaporation is not suppressed as much as predicted by climate models and possibly not suppressed at all. Suppression can't make surface and TOA fluxes agree.

Dec 7, 2015 at 7:35 PM | Unregistered CommenterFrank

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