Climate science from climate scientists...
Guest commentary by Georg Feulner
During a meeting of the Solar Physics Division of the American Astronomical Society, solar physicists have just announced a prediction that the Sun might enter an extended period of low activity (a ‘grand minimum’) similar to the Maunder Minimum in the 17th century. In this post I will explore the background of this announcement and discuss implications for Earth’s climate.
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New results from the University of Aarhus in Denmark and the Danish National Space Institute allegedly show that particles from space create cloud cover, according to a recent press release. And the Physics World magazine (May, 2011) report that the
researchers say this is the best experimental evidence yet that the Sun influences the climate by altering the intensity of the cosmic-ray flux reaching the Earth’s surface.
Quite spectacular claims! So let’s see what is the source of this information.
The basis for the statements was a recent paper published in GRL by Enghoff et al. The key points in the paper are stated as: (a) Cosmic rays increase nucleation rate, (b) A particle beam is not needed, for experiments, and (c) Ions are important for atmospheric nucleation rate. But where is the link to real clouds?
This morning one of the most important (and most delayed) satellite launches in ages took place. The mission was to launch the Glory satellite into a polar orbit, where three key instruments would have been looking at solar irradiance, aerosols and clouds. Unfortunately, one of the stages failed to separate and the satellite did not make orbit.
The irradiance measurements were to be an important continuation of the SORCE mission results, and are needed to stably continue the Total Solar Irradiance (TSI) timeseries. However the big new measurements were those associated with the Aerosol Polarimeter Sensor (APS). A similar instrument has flown in space twice before (the French-developed POLDER instrument), but unfortunately only for short periods. Its uniqueness lies in its ability to detect aerosols over bright surfaces (like land), and more importantly, to distinguish what kind of aerosols it is seeing. (Update: There is a third POLDER instrument, PARASOL, that is currently in orbit, see comments).
It may seem surprising, but despite many different attempts, almost all remote sensing of aerosols from space is only capable of detecting the total optical depth of all aerosols. MISR can provide some discrimination in special cases (picking out dust via a retrieval of non-spherical particles, or using the single scattering albedo to distinguish black carbon), but overall the estimates mix up sulphates, dust, black carbon, sea salt, nitrates and secondary organics. These originate from different processes, have different properties and different impacts on both radiation and clouds. Sea salt comes from sea spray over the oceans, dust from dry desert areas, black carbon from burning of forests and fossil fuels, sulphates derive from ocean plankton and burning coal, nitrates derive from fertiliser use, car exhausts and lightning, and secondary organics come from the stew of volatile organic compounds from industrial and natural sources alike. There are also pollen, and fat particles from outdoor cooking etc.
Because we can’t easily distinguish what’s what from space, we don’t have good global coverage of exactly how much of the aerosol is anthropogenic, and how much is natural. That uncertainty is a big player in the overall uncertainty in the human caused aerosol radiative forcing. Similarly, we have not been able to tell how much of the aerosol is capable of interacting with liquid or ice clouds (which depends on the different aerosols’ affinity for water), and that impacts our assessment of the aerosol indirect effect. These uncertainties are reflected in the model simulations of aerosol concentrations which all show similar total amounts, but have very different partitions among the different types.
The APS technology is a big step forward on these issues. It turns out that while the reflected SW from many different aerosols is similar, the polarisation of that reflected light depends quite strongly on what kind of aerosol it is. This varies depending on the angle at which the light is shining, So by scanning through the angles and measuring the polarisation, we can get a better constraint on the distribution of key aerosols. Scientists have already been working with aircraft mounted versions of the instrument, and this will continue.
The story of how this launch actually happened is very long and twisted, and needless to say, has taken far longer than anyone envisaged at the start (over a decade ago). With the failure to make orbit this morning, the wait will unfortunately go on.
This is of course a huge setback for the mission team (many of whom I know), and I can only imagine how frustrating this must be. The loss of OCO two years ago was due to a similar problem, though 3 launches since then have been successful (and the same system is being replicated as OCO-2). With the postponement of CLARREO in the proposed 2012 budget, there is a huge hole building in the US contribution to Earth and Sun observing systems.
Working from space is hard, expensive and risky. We cannot take it for granted, and yet we need that information more than ever.
When you analyse your data, you usually assume that you know what the data really represent. Or do you? This has been a question that over time has marred studies on solar activity and climate, and more recently cosmic rays and clouds. And yet again, this issue pops up in two recent papers; One by Feulner (‘The Smithsonian solar constant data revisited‘) and another by Legras et al. (‘A critical look at solar-climate relationships from long temperature series.’). Both these papers show how easily it is to be fooled by your data if you don’t know what they really represent.
It’s again time for one of those puzzling results that if they turn out to be true, would have some very important implications and upset a lot of relatively established science. The big issue of course is the “if”. The case in question relates to some results published this week in Nature by Joanna Haigh and colleagues. They took some ‘hot off the presses’ satellite data from the SORCE mission (which has been in operation since 2003) and ran it through a relatively complex chemistry/radiation model. These data are measurements of how the solar output varies as a function of wavelength from an instrument called “SIM” (the Spectral Irradiance Monitor).
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) Una traducción en español está disponible aquí.
Four new papers discuss the relatiosnhip between solar activity and climate: one by Judith Lean (2010) in WIREs Climate Change, a GRL paper by Calogovic et al. (2010), Kulmala et al. (2010), and an on-line preprint by Feulner and Rahmstorf (2010). They all look at different aspects of how changes in solar activity may influence our climate.
We received a letter with the title ‘Climate Change: The Role of Flawed Science‘ which may be of interest to the wider readership. The author, Peter Laut, is Professor (emeritus) of physics at The Technical University of Denmark and former scientific advisor on climate change for The Danish Energy Agency. He has long been a critic of the hypothesis that solar activity dominates the global warming trend, and has been involved in a series of heated public debates in Denmark. Even though most of his arguments concern scientific issues, such as data handling, and arithmetic errors, he also has much to say about the way that the debate about climate change has been conducted. It’s worth noting that he sent us this letter before the “CRU email” controversy broke out, so his criticism of the IPCC for being too even handed, is ironic and timely.
Update – the link in the letter is now fixed. -rasmus
I believe the idea that galactic cosmic rays (GCR) play a role for the present global warming is unlikely to fade soon, despite a growing number of scientific arguments that normally would falsify a hypothesis and lay it dead (see links here and here). Despite all the arguments against the role of GCR, there was a solicited talk about ‘cosmoclimatology’ at the European Meteorological Society’s (EMS) annual meeting in Toulouse. Henrik Svensmark is further invited by the Norwegian Academy of Science and Letters (NASL) to provide an introduction to their seminar on climate. So why is the GCR-hypothesis still perceived as an interesting explanation?
In a new GRL paper, Svensmark et al., claim that liquid water content in low clouds is reduced after Forbush decreases (FD), and for the most influential FD events, the liquid water content in the oceanic atmosphere can diminish by as much as 7%. In particular, they argue that there is a substantial decline in liquid water clouds, apparently tracking a declining flux of galactic cosmic rays (GCR), reaching a minimum days after the drop in GCR levels. The implication would be that GCR can affect climate through modulating the low-level cloudiness. The analysis is based on various remote sensing products.
