Inger Hanssen-Bauer

HOMOGENEITY ADJUSTMENTS OF IN SITU ATMOSPHERIC CLIMATE DATA: A REVIEW

Long-term in situ observations are widely used in a variety of climate analyses. Unfortunately, most decade- to century-scale time series of atmospheric data have been adversely impacted by inhomogeneities caused by, for example, changes in instrumentation, station moves, changes in the local environment such as urbanization, or the introduction of different observing practices like a new formula for calculating mean daily temperature or different observation times. If these inhomogeneities are not accounted for properly, the results of climate analyses using these data can be erroneous. Over the last decade, many climatologists have put a great deal of effort into developing techniques to identify inhomogeneities and adjust climatic time series to compensate for the biases produced by the inhomogeneities. It is important for users of homogeneity-adjusted data to understand how the data were adjusted and what impacts these adjustments are likely to make on their analyses. And it is important for developers of homogeneity-adjusted data sets to compare readily the different techniques most commonly used today. Therefore, this paper reviews the methods and techniques developed for homogeneity adjustments and describes many different approaches and philosophies involved in adjusting in situ climate data.

Temperature and precipitation variations in Norway 1900–1994 and their links to atmospheric circulation

The main aim of the present study was to identify to what degree decadal scale variability and long-term trends in temperature and precipitation in Norway can be attributed to variations in the dominating atmospheric circulation patterns. Empirical models were developed and tested on monthly series of temperature and precipitation in different regions in Norway. The monthly mean sea level pressure (SLP) field over the northern North Atlantic and northern Europe was used as a predictor. Principal components (PCs) deduced from this field were used as a basis for stepwise multiple regression analysis. The downscaling models were developed using 1925–1969 as a training period, while 1900–1924 and 1970–1994 were used as validation periods. Model testing revealed that the temperature variability during 1970–1994 in most cases was better simulated than the variability during 1900–1924. The models reproduced most of the observed trends and decadal scale variability from 1940 to present. They also reproduced the precipitation trends in western Norway before 1940. However, the temperature increase observed over all the country in 1900–1940 was not reproduced. Nor was the increased winter precipitation in southeastern Norway during the same period. It is concluded that the temperature and precipitation changes observed in Norway during the last 40 years can mainly be attributed to variations in the SLP field. Variations in the precipitation conditions in the eastern parts of the country, and in temperature all over the country, during 1900–1940 are probably connected to changes in external forcings and/or atmosphere–ocean interactions. Copyright

Past and future climate variations in the Norwegian Arctic: overview and novel analyses

Sparse stations and serious measuring problems hamper analyses of climatic conditions in the Arctic. This paper presents a discussion of measuring problems in the Arctic and gives an overview of observed past and projected future climate variations in Svalbard and Jan Mayen. Novel analyses of temperature conditions during precipitation and trends in fractions of solid/liquid precipitation at the Arctic weather stations are also outlined. Analyses based on combined and homogenized series from the regular weather stations in the region indicate that the measured annual precipitation has increased by more than 2.5% per decade since the measurements started in the beginning of the 20th century. The annual temperature has increased in Svalbard and Jan Mayen during the latest decades, but the present level is still lower than in the 1930s. Downscaled scenarios for Svalbard Airport indicate a further increase in temperature and precipitation. Analyses based on observations of precipitation types at the regular weather stations demonstrate that the annual fraction of solid precipitation has decreased at all stations during the latest decades. The reduced fraction of solid precipitation implies that the undercatch of the precipitation gauges is reduced. Consequently, part of the observed increase in the annual precipitation is fictitious and is due to a larger part of the “true“ precipitation being caught by the gauges. With continued warming in the region, this virtual increase will be measured in addition to an eventual real increase.

Homogenizing Long Norwegian Precipitation Series

Abstract The standard normal homogeneity test has been applied to 165 Norwegian precipitation series of 75 years or more. Of these series, 50 were found to be homogeneous, while 79 became homogeneous after being adjusted for a single inhomogeneity. Almost 50% of the inhomogeneities were caused by relocation of the precipitation gauge. Other reasons for inhomogeneities were changes in the immediate environment (trees, buildings) and changes in instruments (windshield, new gauge type). About 80% of the inhomogeneities could be traced to information in the station history flies. Most of the inhomogeneities caused by changes in instrumentation led to increased gauge catch. There was a similar tendency for inhomogeneities caused by changes in environment. Consequently, trend studies based on groups of untested series may give dubious trends. Homogeneity testing and station history archives are essential tools for finding the real trends and fluctuations in precipitation series.

Impact of climate change on agriculture in Northern Norway and potential strategies for adaptation

This study evaluates the effects of climate change on agriculture in Northern Norway. It is based on downscaled climate projections for six different municipalities combined with interviews with farmers, advisors and administrative personnel in these municipalities. The projections document large climatic differences both between and within the different municipalities. The main predicted climatic changes include increasing temperatures and precipitation as well as increased frequency of certain types of extreme weather events. Despite challenges such as unstable winters, increased autumn precipitation and possibly more weeds and diseases, a prolongation of the current short growth season together with higher growth temperatures can give new opportunities for agriculture here. The impacts are expected to differ both within and between municipalities and will require tailored adaptive strategies. Most of these however should pose no difficulty implementing, having an agronomical basis that farmers are accustomed to cope with.

Recent change - atmosphere

This chapter examines past and present studies of variability and changes in atmospheric variables within the North Sea region over the instrumental period; roughly the past 200 years. The variables addressed are large-scale circulation, pressure and wind, surface air temperature, precipitation and radiative properties (clouds, solar radiation, and sunshine duration). Temperature has increased everywhere in the North Sea region, especially in spring and in the north. Precipitation has increased in the north and decreased in the south. There has been a north-eastward shift in storm tracks, which agrees with climate model projections. Due to large internal variability, it is not clear which aspects of the observed changes are due to anthropogenic activities and which are internally forced, and long-term trends are difficult to deduce. The number of deep cyclones seems to have increased (but not the total number of cyclones). The persistence of circulation types seems to have increased over the past century, with ‘more extreme’ extreme events. Changes in extreme weather events, however, are difficult to assess due to changes in instrumentation, station relocations, and problems with digitisation. Without thorough quality control digitised datasets may be useless or even counterproductive. Reanalyses are useful as long as biases introduced by inhomogeneities are properly addressed. It is unclear to what extent circulation over the North Sea region is controlled by distant factors, especially changes in Arctic sea ice.

Communication and use of climate scenarios for climate change adaptation in Finland, Sweden and Norway

This paper assesses the communication and the use of climate scenarios at the science–science and science–policy interface in Finland, Sweden and Norway. It is based on document analysis and stakeholder questionnaires. The questionnaires targeted three stakeholder groups, all engaged in the communication and the use of climate scenario information: climate scenario producers; impact, adaptation and vulnerability (IAV) experts; and policy-makers. The respondents were asked to identify issues associated with the communication of scenarios and other needs pertaining to the usefulness and availability of such information. Despite the relatively long history of climate change adaptation in the three countries, climate scenarios are not utilised to their full potential. Climate scenarios have been used in awareness raising, problem understanding and strategy development. However, far less examples can be found on adaptation actions, particularly on harnessing the benefits of climate change. The communication between climate scenario producers and IAV experts functions well; however, communication between climate researchers and policy-makers is less efficient. Each country has developed boundary services to enhance dissemination of the climate scenario information to policy-makers. They are cost-efficient but do not necessarily enhance the comprehension of the information and encourage the actual dialogue between scenario producers and the end-users. Further translation of scenario information to impact and vulnerability estimates together with established boundary work could improve the use of climate research information. As adaptation policy in these countries further progresses towards implementation, there are increasing expectations of support from research, further challenging the communication of climate scenarios.

New Norwegian climate normals – but has the climate changed?

The new normal values for the period 1961–1990 will be used as a reference for weather conditions in years to come. There has been a drop in temperature in most parts of Norway since the previous normal period 1931–1960. Annual precipitation has increased in most parts of the country. Moving averages indicate that a 30-year period is too short a time to obtain stable mean values of climatic parameters, and thus the standard normal values may be quite ‘abnormal.’ Trend-analysis is used to describe temperature and precipitation variations in Norway during the last 100 years.

Relationships between vegetation, air and soil temperatures on Norwegian mountain summits

ABSTRACT Geographic variations in air and soil temperatures are dependent on several biotic and abiotic factors. Air temperature has mostly been used to characterize thermal conditions for plant life, and studies of bioclimatic gradients. From a biological point of view, it is also essential to know to what extent soil temperature is coupled with air temperature. In this study, we have quantified the deviations between soil and air temperatures along gradients in latitude, altitude, and possible effects of the vegetation. Sixteen different temperature variables were estimated from 49 vegetation plots on 19 mountain summits along the high mountain range in Norway, ranging from 230 to 1780 m a.s.l., and from 59°N to 71°N. Soil and air temperature variables were estimated from the study plots during one year. All air and soil temperature variables were significantly correlated, but the rate of explanation was mostly relatively low (37.0–60.0%), except during the growing season. Start of the growing season, determined by air or soil temperatures, could deviate by 38 days mainly due to effects of frozen soils. Vegetation composition, especially the lichen cover, had a major impact on soil temperature, Dwarf shrub cover increased significantly with increasing July temperature. Lichen abundance and degree of soil frost were strongly correlated, and explained a major part of the variation in soil temperatures. The study indicates that air temperature is generally a poor proxy for soil temperature in cold areas, except during July.

Climate variation in the European sector of the Arctic: Observations and scenarios

Global climate models typically indicate that increased concentrations of atmospheric greenhouse gases will lead to a larger temperature increase at high northern latitudes than anywhere else in the world (Cubasch et al. 2001, Räisänen 2003). On the other hand, a majority of the models indicate an area of minimum temperature response around southern Greenland. Large gradients in warming rates are thus projected in the Arctic. The mean temperature in the Arctic did increase during the 20 century (e.g. Polyakov et al. 2003), but there are regional differences within the area. This paper is focused on the observed and modeled atmospheric climate in the European sector of the Arctic from 1900 to 2100. Are the observed changes in accordance with results from climate models? And what are the prospects for the future climate?