Chris Folland | The University Of East Anglia (original) (raw)

Papers by Chris Folland

Environmental Research Letters, 2017

Earth System Dynamics Discussions, 2019

The realistic simulation of the summer Mediterranean climate requires not only refined spatial sc... more The realistic simulation of the summer Mediterranean climate requires not only refined spatial scales, but also an adequate representation of land-atmosphere interactions and teleconnections. Addressing all of these issues remains a challenge for most of the CMIP3/CMIP5 generation models. In this study we analyze highresolution (~0.5° lat x lon) RCP8.5 future projections of the Geophysical Fluid Dynamics Laboratory CM2.5 model with a new incorporated land model (LM3). The simulated regional future changes suggest pronounced warming and drying over most parts of the Mediterranean. However the changes are distinctively less radical when compared with the CMIP5 multimodel ensemble. Moreover, changes over the Southeast (off the coast area of the Balkans) and Central Europe indicate not only a very modest warming, compared to the CMIP5 projections, but also wetting tendencies. The difference of CM2.5 projections of future changes over previous-generation models highlights the importance of a) a correctly projected magnitude of changes of the North Atlantic Oscillation and its regional impacts, which have the capacity to partly offset the anthropogenic warming and drying over the western and central Mediterranean; b) a refined representation of land surface-atmospheric interactions, which are a governing factor for thermal-and hydro-climate over Central and Southeastern Europe. The CM2.5 projections also indicate a maximum of warming (Levant) and drying (Asia Minor) over the eastern Mediterranean. The changes derived in this region indicate a decreasing influence of atmospheric dynamics in maintaining the regional temperature and precipitation balance and instead an increasing influence of local surface temperature on the local surface atmospheric circulation.

Hydrological Sciences Bulletin, 1980

Atmosphere

We compare the Arctic amplification (AA) produced by the two Community Earth System Models CESM1 ... more We compare the Arctic amplification (AA) produced by the two Community Earth System Models CESM1 and CESM2, members of the CEMIP5 (Coupled Models Intercomparison Project phase 5) and CEMIP6 collections, respectively. We find that the CESM1 model reproduces the recent high values of the AA deduced from the observed temperature much better than the CESM2. The correlation coefficient within the 1970–2012 time period between CESM1-simulated AA and the observed one is 0.47, while the CESM2 simulation leads to an anticorrelation of r = −0.53. Even the more successful model (CESM1) is not able to reproduce recent high AA values of 4–5. The main cause of this failure is the model’s overestimate of the rate of increase in the mean global temperature in years post 1990. When the CESM1 model’s simulated trend of the mean global temperature is replaced in the expression for the AA by the observed temperature trend, the correlation coefficient increases from 0.47 to 0.75. The CESM1 model is amon...

Annals of Geophysics, 2009

An analysis of observations from 1948-1998 suggests that the atmosphere in the North Atlantic reg... more An analysis of observations from 1948-1998 suggests that the atmosphere in the North Atlantic region does respond to North Atlantic Sea-Surface Temperatures (SSTs) throughout the annual cycle. In the subtropics, high geopotential heights are seen to be a local response to warm SSTs. In winter, the North Atlantic Oscillation responds to a «tripole» pattern in North Atlantic SSTs. In summer, anticyclonicity over the U.K. is seen downstream of warm SST anomalies off Newfoundland and is possibly also related to warm subtropical SSTs. Such responses imply a degree of seasonal predictability and help quantify the strength of natural ocean-atmosphere coupled modes of variability. The average of an ensemble of 10 simulations of the HadAM3 atmospheric model forced with observed SSTs for the same period produces robust ocean-forced responses which agree well with those identifi ed in the observations and with a previous model. The agreement is encouraging as it confi rms the physical signifi cance of the observational results and suggests that the model responds with the correct patterns to SST forcing. In the subtropics, the magnitude of the ensemble mean response is comparable with the observational response. In the extratropics, the magnitude of the model response is about half that of the observations. Although atmospheric internal variability may have affected the observed atmospheric patterns and there are considerations regarding the lack of two-way air-sea interaction with an atmospheric model, it is suggested that the model's extratropical response may be too weak. The 10 individual simulations of HadAM3 and 28 50-year periods of the ocean-atmosphere model, HadCM3, display similar results to each other with generally weaker ocean-forced links than observed. Seasonal predictability may, therefore, be too low in HadCM3 and low-frequency coupled modes under-represented. A moderate increase in the extratropics in the sensitivity of surface heat fl uxes to surface temperatures is one possibility for improving these model defi ciencies.

Winter temperatures and precipitation amounts in Europe are known to be quite strongly influenced... more Winter temperatures and precipitation amounts in Europe are known to be quite strongly influenced by the North Atlantic Oscillation (NAO) and may also be affected by other circulation and sea-surface temperature (SST) patterns. Summer precipitation totals in Europe as a whole are less influenced by the summer NAO (though the UK is an exception) but show marked multi decadal variability and are related to global-scale SST and atmospheric circulation variability. Such observed links have important implications for predictability. So a clear goal of EMULATE has been to document these relationships, using new and extended datasets of daily pressure, temperature and precipitation, in addition to the existing, high quality SST analysis, HadISST [Rayner et al., 2003].

Weather and Climate Extremes, 2019

There is a growing research interest in understanding extreme weather in the context of anthropog... more There is a growing research interest in understanding extreme weather in the context of anthropogenic climate change, posing a requirement for new tailored climate data products. Here we introduce the Climate of the 20th Century Plus Detection and Attribution project (C20C + D&A), an international collaboration generating a product specifically intended for diagnosing causes of changes in extreme weather and for understanding uncertainties in that diagnosis. The project runs multiple dynamical models of the atmosphere-land system under observed historical conditions as well as under naturalised versions of those observed conditions, with the latter representing how the climate system might have evolved in the absence of anthropogenic interference. Each model generates large ensembles of simulations with different initial conditions for each historical scenario, providing a large sample size for understanding interannual variability, long-term trends, and the anthropogenic role in rare types of weather. This paper describes the C20C + D&A project design, implementation, strengths, and limitations, and also discusses various activities such as this special issue of Weather and Climate Extremes dedicated to "First results of the C20C + Detection and Attribution project". 1. Motivation Over the past decade and a half, many climate researchers have perceived a demand for better understanding of the current extreme weather hazard, as well as of the contribution of long-term climate trends to that hazard (Stott et al., 2013; National Academies of Sciences, Engineering, and Medicine, 2016; Stott et al., 2016). For lack of a better term, we will refer to both questions as dealing with "event attribution". The need for event attribution was first articulated within the context of informing court decisions on tort claims (Allen, 2003; Allen and Lord, 2004; Allen et al., 2007). More recently, event attribution has also been suggested as information required for funding decisions involved in the United Nations Framework Convention on Climate Change "Loss and Damage" (L&D) activity (and other L&D activities) (Pall et al., 2011; James et al.

Science advances, 2018

The time series of monthly global mean surface temperature (GST) since 1891 is successfully recon... more The time series of monthly global mean surface temperature (GST) since 1891 is successfully reconstructed from known natural and anthropogenic forcing factors, including internal climate variability, using a multiple regression technique. Comparisons are made with the performance of 40 CMIP5 models in predicting GST. The relative contributions of the various forcing factors to GST changes vary in time, but most of the warming since 1891 is found to be attributable to the net influence of increasing greenhouse gases and anthropogenic aerosols. Separate statistically independent analyses are also carried out for three periods of GST slowdown (1896-1910, 1941-1975, and 1998-2013 and subperiods); two periods of strong warming (1911-1940 and 1976-1997) are also analyzed. A reduction in total incident solar radiation forcing played a significant cooling role over 2001-2010. The only serious disagreements between the reconstructions and observations occur during the Second World War, espec...

Atmospheric Science Letters, 2017

We present a case study of long range forecasts for Northern Hemisphere winter 2015/2016. This wi... more We present a case study of long range forecasts for Northern Hemisphere winter 2015/2016. This winter produced the strongest El Niño event since 1997/1998 and equatorial Pacific sea surface temperature anomalies exceeded 3 ∘ C. Other factors relevant to the Northern Hemisphere extratropical atmosphere circulation included a strong westerly phase of the Quasi-Biennial Oscillation (QBO) and very strong winds in the stratospheric polar night jet in early winter. At the surface, intense cyclonic extratropical circulation anomalies occurred in early winter in both the North Pacific and North Atlantic, consistent with known teleconnections to these phases of El Niño-Southern Oscillation, the QBO and the polar night jet. The midlatitude flow was very westerly in early winter and less westerly and sometimes northerly in late winter, when sudden stratospheric warming events also occurred. We show that initialised climate predictions were able to capture the winter mean flow pattern at seasonal lead times from well before the start of winter. In this special case, not only the winter mean flow pattern, but also some aspects of the sub-seasonal evolution were skilfully predicted. We show that the winter of 1982/1983 was closely analogous to winter 2015/2016 in both the predictable driving factors and the forecast winter circulation. This case study adds to the evidence that the north Atlantic circulation can be predictable on seasonal timescales and advance warning of the increased risk of intense rainfall and storminess which caused extreme flooding in the UK in December was possible in this case.

International Geophysics, 2002

This paper summarizes an invited presentation given at the historic "Meteorology at the Millenniu... more This paper summarizes an invited presentation given at the historic "Meteorology at the Millennium" Conference in July 2000, which marked the 150 th anniversary of the Royal Meteorological Society. It begins with a broad review of the North Atlantic Oscillation (NAO) and the mechanisms that might influence its phase and amplitude on decadal and longer time scales. New results are presented which suggest an important role for tropical ocean forcing of the unprecedented trend in the wintertime NAO index over the past several decades. We conclude with a brief discussion of a recent significant change in the pattern of the summertime atmospheric circulation over the North Atlantic.

Climate Dynamics, 2015

straightforward manner, and can be used to evaluate the skill of dynamical decadal prediction sys... more straightforward manner, and can be used to evaluate the skill of dynamical decadal prediction systems. Composites of SST and mean sea level pressure anomalies reveal that the IPO has maintained a broadly stable structure across the seven most recent positive and negative epochs that occurred during 1870-2013. The TPI is shown to be a robust and stable representation of the IPO phenomenon in instrumental records, with relatively more variance in decadal than shorter timescales compared to Niño 3.4, due to the explicit inclusion of off-equatorial SST variability associated with the IPO.

International Seminar on Nuclear War and Planetary Emergencies — 30th Session, 2004

This is the print version of the Skeptical Science article 'It's not happening', which can be fou... more This is the print version of the Skeptical Science article 'It's not happening', which can be found at http://sks.to/warming. Evidence for global warming What The Science Says: There are many lines of independent empirical evidence for global warming, from accelerated ice loss from the Arctic to Antarctica to the poleward migration of plant and animal species across the globe. Climate Myth: It's not happening "...these global warming studies that now we're seeing (are) a bunch of snake oil science." (Sarah Palin)

Weather, 2002

Observed Climate Variability and Change Changes in temperature-related variables • Alpine and con... more Observed Climate Variability and Change Changes in temperature-related variables • Alpine and continental glaciers have extensively retreated in response to 20th century warming. Glaciers in a few maritime regions are advancing, mainly due to increases in precipitation related to atmospheric circulation changes, e.g., Norway, New Zealand. • The duration of Northern Hemisphere lake-ice and river-ice cover over the past century, or more, shows widespread decreases averaging to about two fewer weeks of ice cover. • There is a highly significant interannual (+0.6) and multi-decadal correlation between increases in the Northern Hemisphere spring land temperature and a reduction in the Northern Hemisphere spring snow cover since data have been available (1966). Snow cover extent has decreased by about 10% since 1966. • No systematic changes in the frequency of tornadoes, thunder days, or hail events are evident in the limited areas analysed. 106 Observed Climate Variability and Change Box 2.1: Urban Heat Island and the Observed Increases in Land Air Temperature. There are two primary reasons why urban heat islands have been suspected as being partially responsible for the observed increases in land air temperatures over the last few decades. The first is related to the observed decrease in the diurnal temperature range and the second is related to a lower rate of warming observed over the past twenty years in the lower troposphere compared with the surface. Since the 1950s both daily maximum and minimum temperatures are available over more than 50% of the global land area. These data indicate that on average the mean minimum temperature has increased at nearly twice the rate of the maximum temperature, reducing the daily temperature range by about 0.8°C over these areas. This has raised questions related to whether the growth of urban heat islands may be responsible for a substantial portion of the observed mean temperature increase, because it is well-known that compared to non-urban areas urban heat islands raise night-time temperatures more than daytime temperatures. Nonetheless, the relatively strong correlation between observed decreases in the daily temperature range with increases of both precipitation (leading to more moist surface conditions) and total cloud amount support the notion that the reduction in diurnal temperature range is in response to these physical changes. Since 1979 satellite observations and weather balloons (which generally agree well) show substantially less warming of the global lower troposphere (around 2 km) than surface temperatures (0.03 and 0.04°C/decade, respectively, compared to 0.16°C/decade at the surface). However, over the Northern Hemisphere land areas where urban heat islands are most apparent, both the trends of lowertropospheric temperature and surface air temperature show no significant differences. In fact, the lower-tropospheric temperatures warm at a slightly greater rate over North America (about 0.28°C/decade using satellite data) than do the surface temperatures (0.27°C/decade), although again the difference is not statistically significant. In the global average, the trend differences arise largely from the tropical and subtropical oceans. In many such regions, the near-surface marine air temperatures tend to be cool and dense compared with conditions aloft, allowing for the lapse rate with height, disconnecting near-surface (up to about 1 km) conditions from higher layers in the atmosphere. Thus the surface marine layer and the troposphere above can have differing variations and trends. Clearly, the urban heat island effect is a real climate change in urban areas, but is not representative of larger areas. Extensive tests have shown that the urban heat island effects are no more than about 0.05°C up to 1990 in the global temperature records used in this chapter to depict climate change. Thus we have assumed an uncertainty of zero in global land-surface air temperature in 1900 due to urbanisation, linearly increasing to 0.06°C (two standard deviations 0.12°C) in 2000.

Journal of Geophysical Research: Atmospheres, 2001

We describe the contemporary hydrography of the pan‐Arctic land area draining into the Arctic Oce... more We describe the contemporary hydrography of the pan‐Arctic land area draining into the Arctic Ocean, northern Bering Sea, and Hudson Bay on the basis of observational records of river discharge and computed runoff. The Regional Arctic Hydrographic Network data set, R‐ArcticNET, is presented, which is based on 3754 recording stations drawn from Russian, Canadian, European, and U.S. archives. R‐ArcticNET represents the single largest data compendium of observed discharge in the Arctic. Approximately 73% of the nonglaciated area of the pan‐Arctic is monitored by at least one river discharge gage giving a mean gage density of 168 gages per 106 km2. Average annual runoff is 212 mm yr−1 with approximately 60% of the river discharge occurring from April to July. Gridded runoff surfaces are generated for the gaged portion of the pan‐Arctic region to investigate global change signals. Siberia and Alaska showed increases in winter runoff during the 1980s relative to the 1960s and 1970s during...

Journal of Climate, 2005

Rainfall variability occurs over a wide range of temporal scales. Knowledge and understanding of ... more Rainfall variability occurs over a wide range of temporal scales. Knowledge and understanding of such variability can lead to improved risk management practices in agricultural and other industries. Analyses of temporal patterns in 100 yr of observed monthly global sea surface temperature and sea level pressure data show that the single most important cause of explainable, terrestrial rainfall variability resides within the El Niño–Southern Oscillation (ENSO) frequency domain (2.5–8.0 yr), followed by a slightly weaker but highly significant decadal signal (9–13 yr), with some evidence of lesser but significant rainfall variability at interdecadal time scales (15–18 yr). Most of the rainfall variability significantly linked to frequencies lower than ENSO occurs in the Australasian region, with smaller effects in North and South America, central and southern Africa, and western Europe. While low-frequency (LF) signals at a decadal frequency are dominant, the variability evident was E...

International Journal of Climatology, 2011

International Journal of Climatology, 2005

Analyses of simulations of variations in global and large‐regional land surface air temperature (... more Analyses of simulations of variations in global and large‐regional land surface air temperature (LSAT) for 1872–1998 using the HadAM3 atmospheric general circulation model are reported. The analyses are designed to test the accuracy of bias corrections to sea‐surface temperature (SST) used in the Hadley Centre's global sea ice and SST (GISST3.1) data set, the more recent Hadley Centre sea ice and SST (HadISST) data set, and in the underlying Met Office historical SST (MOHSST and HadSST1) data sets. The tests are important because SST corrections considerably affect estimates of the magnitude of global warming since the late 19th century. Two ensembles of simulations were created using GISST3.1 as the lower boundary condition. The first ensemble, of six integrations, was forced using GISST with bias‐corrections applied from 1871 until 1941, and was continued with no bias corrections to 1998. A second ensemble of four integrations, for 1871 to 1941, was forced with uncorrected GIS...