Scottish Government

ANNEX A: SCOTLAND'S CHANGING CLIMATE

A.1 Modelling of past climate trends can be a useful tool in developing climate management strategies. A recent survey conducted by the Scottish Government of selected organizations in Scotland suggests that the most important information for developing their weather management strategies was weather information from the previous 10-20 years and future forecasts for the next 20 years. However, it is important to recognise that it is very unlikely there will be a linear continuation of historical climate trends. The degree of change seen in past climate trends is unlikely to match the degree of change in future climate trends as higher temperatures in the future will increase the chance of triggering abrupt and large-scale changes.

A.2 Modelling of future climate scenarios is becoming more advanced, particularly in recognizing the inherent uncertainty of future emissions production. In late 2008, UKCIP will release the fifth generation of climate scenarios produced for the UK. The new scenarios, called UK 21 ^st Century Climate Scenarios²² or UKCIP08 for short, reflect changing user requirements and advances in climate science and computer power. The 2008 scenarios do not conflict with those produced in 2002, but will give us a greater level of detail and, with that, increased usability. There is a wide spectrum of user needs for climate scenarios and the UKCIP02 scenarios have been employed for a broad range of uses. These can be crudely divided into those associated with specific research, policy or design decisions, and those associated with general awareness-raising and communication.

A.3UKCIP consulted with a wide range of stakeholders to determine user preferences for the format and delivery of UKCIP08 and information will be provided through three
key products:

• Probabilistic climate projections: information on modelled future climate change for all 25 x 25 km UK land grid squares, provided in probabilistic terms
• Marine projections: information on modelled future changes above and below the surface of sea areas around the UK
• Historical climate information: information on present UK climate and recent trends, based on observations. This report is already available on the UKCIP website. ²³

A.4 For the purposes of this consultation document, an overview of a number of key climate variables has been presented in terms of observed trends and likely future scenarios. This overview has been informed by the Scotland & Northern Ireland Forum for Environmental Research's publication A Handbook of Climate Trends Across Scotland²⁴ and UK Climate Impacts Programme's ( UKCIP) climate scenarios released in 2002. ²⁵

Historical climate trends in Scotland

A.5 The Handbook of Climate Trends Across Scotland²⁶ analysed climate data recorded over the past century to identify trends in climate change. This work provides a valuable benchmark against which we can measure future climate change. The key changes recorded across Scotland since 1961 include:

Temperature: Temperatures have risen in every season and in all parts of Scotland;

Rainfall: Scotland had become 20% wetter by 2004, with an increase of almost 70% in precipitation in northern Scotland;

Snow cover: The snow season has shortened across the country, which the season starting later and finishing earlier in the year. The greatest reductions have occurred in northern and western Scotland;

Growing season: The growing season length has increased significantly, with the greatest change occurring at the beginning of the season; and

Days of frost: There has been more than a 25% reduction in the number of days of frost (both air and ground frost) across the country.

Future climate scenarios for Scotland

A.6 The most recent set of climate scenarios for the UK were released in 2002 ²⁷. Assuming a future with medium-high global emissions production, changes to Scotland's climate are likely to include:

Temperature: Annual temperature averaged across Scotland may rise by up to 3.5 ^oC in the summer and
2.5 ^oC in the winter by the 2080s;

Rainfall: While winters may become wetter, summers will become generally drier across Scotland by the 2080s;

Snow cover: Average snowfall may decrease, perhaps by up to 90% less depending on the location, and snowless winters may become normal in some parts by the 2080s;

Growing season: Scotland's growing season may become longer, by between 20 and 60 days by 2080; and

Sea level: Scotland's sea levels may rise relative to the land, in some areas. By 2080 the current estimates range between 0 and 600 mm sea level rise.

A.7 An overview of historical trends and future scenarios for these climate variables are further explored in the remainder of this chapter. Where results for Scotland have been disaggregated below the national level, they are presented as the following regions.

Figure A.1: Map of Scotland showing boundaries of the three regions as defined in the following climate trends and scenarios (North, West and East Scotland).

Average Temperatures

Key message: Temperatures are expected to rise over Scotland, with increases being greatest during summer and autumn months by the 2080s. ²⁸

Figure A.2: The average temperature (in 0C) each year for Scottish regions, from 1914 to 2004, with smoothed curves to show a running average. The vertical dashed line marks 1961.

Source: Scotland and Northern Ireland Forum for Environmental Research, A Handbook of Trends Across Scotland, 2006

Previous climate trends

• The average annual temperatures in each region are now higher than at any other time since 1914.
• The analysis from 1914 to 2004 shows a trend of increases in
  annual temperature, particularly in East and West Scotland. This matches information about temperature increases in the UK
  and around the world.
• Temperature increases have been greater since 1961 than between 1914 and 1961.
• The increases in temperature we have seen since 1961 also are part of a trend in each region and every season, apart from winter in North Scotland.
• The increases are smallest during autumn and there has been some slight cooling in Highland areas during autumn.
• The greatest increases have taken place during spring and winter and the largest in southern and eastern Scotland in winter.
• The northern Outer Hebrides, Shetland and Orkney are warming at a similar level in all seasons.

Future climate scenarios

• Temperatures are expected to rise over Scotland, with greatest increases during summer and autumn months (up to 4 ^0C for the UKCIP02 medium-high emissions scenario by the 2080s).
• In line with the trends we have seen, southern Scotland is expected to warm at a faster rate than the north by the 2080s.

Rainfall

Key message: While overall precipitation amounts are not forecast to change greatly, winters are likely to become wetter while summers become drier than at present by the 2080s. ²⁹

Figure A.3: Precipitation total (in millimetres) each year for Scottish regions, from 1914 to 2004 with smoothed curves to show a running average.

Source: Scotland and Northern Ireland Forum for Environmental Research, A Handbook of Trends Across Scotland, 2006

Previous climate trends

• In each region, and across the country, the change in winter precipitation since 1961 shows a clear upward trend. We can see an increase of almost 70% in winter precipitation in North Scotland.
• In terms of average precipitation, Scotland had become 20% wetter
  by 2004.
• The largest changes have taken place in winter months across all of Scotland, particularly eastern areas. In some areas of the west Highlands and the Hebrides, winter precipitation has more than double since 1961.
• In summer, northern areas of Scotland have become drier since 1961, particularly the north-west. This reduction in summer precipitation is more than 20% in some areas.
• There is a trend of increasing rainfall intensity in both East and West Scotland.

Future climate scenarios

• The UKCIP02 scenarios show relatively little change to average precipitation amounts each year (trend shows increasing totals) but winter months may become wetter (as already seen) with increased intensity of rainfall, while summer months may be drier than at present by 2080.
• The pattern of change may not be the same across Scotland. UKCIP02 estimate eastern Scotland may experience the most extreme percentage changes in precipitation (going against the trend we have seen already), with an increase in winter and a reduction in summer by the 2080s.

Snowfall and snow coverage

Key message: Snowfall is likely to reduce by 50% or more across all of Scotland, particularly in eastern Scotland where it may reduce by up to 90% by the 2080s. ³⁰

Figure A.4: Days of snow cover each year for Scottish regions, from 1961/62 to 2004/05, with smoothed curves showing a running average.

Source: Scotland and Northern Ireland Forum for Environmental Research, A Handbook of Trends Across Scotland, 2006

Previous climate trends

The number of days of snow cover has reduced in each region and in all seasons.

• In winter, the decreases are greater than 25%, and are the largest changes (in terms of total number of days), a decrease of 7 days.
• The largest percentage changes have taken place in spring and autumn, which shows that the snow season is getting shorter.
• The west of the country and particularly the western Highlands show the greatest reduction in snow cover in terms of the number of days. However, you should note that these areas are also those that normally have the largest number days of snow cover.

Future climate scenarios

• The UKCIP02 scenarios assesses snowfall rather than snow cover in the future scenarios. We cannot directly compare this with the information presented on snow cover, but the general reduction is what the UKCIP02 scenarios suggest for the future.
• Winter snowfall may reduce by 50% or more across Scotland by the 2080.
• The most obvious changes are over eastern Scotland, with a possible reduction of over 90% of snowfall by the 2080s.

Growing season

Key message: There is likely to be an increase in the length of the growing season of between 20 and 60 days by the 2080s. ³¹

Figure A.5: Length of the growing season (in days) each year for Scottish regions, from 1961 to 2004, with smoothed curves showing a running average.

Source: Scotland and Northern Ireland Forum for Environmental Research, A Handbook of Trends Across Scotland, 2006

Previous climate trends

• In the early 1960s, typical values were a growing season of about 213 days in East Scotland, 217 days in North Scotland and 237 days in the West.
• All regions have seen an increase of more than four weeks in the length of the growing season since 1961.
• The West has shown the greatest increase and the North the least.
• At a sub-regional level, the greatest increases in the length of the growing season are in coastal areas and the Shetland Islands where the season has extended by two months, or more.
• There is very little change in the length of the growing season evident in some of the mountainous areas and even a reduction of up to eight days shown in a few of the upland areas.

Future climate scenarios

• The UKCIP02 scenarios show an increase in the length of the growing season of between 20 and 60 days by the 2080s.
• The UKCIP02 scenarios suggest the increase will be greater in the east than in the west by the 2080s, but the information from past observations show the opposite pattern.

Days of frost

Key message: Since 1961, there has been more than a 25% reduction in the number of days of frost (both ground and air frost) across the country.

Figure A.6: Days of ground frost for Scottish regions each year from 1961/62 to 2004/05, with smoothed curves showing a running average.	Figure A.7: Days of air frost for Scottish regions each year, from 1961/62 to 2004/05, with smoothed curves showing a running average.

Previous climate trends

• Ground frost, which happens when the minimum grass temperature falls to 0 ^0C or below, is a common event in Scotland, even in the summer.
• Since 1961 there has been a reduction in the number of days of ground frost in every season, and for each of the three Scottish regions.
• At a sub-regional level, the reduction in ground frost days is particularly evident over the western Highlands and Hebrides in spring. However, the number of days of ground frost has actually increased in winter on both the Shetland and Orkney Islands.
• Since 1961, there has been more than a 25% reduction in the number of days each year of air frost. This is part of a downward trend that is clear in all three regions and nationally.
• The largest changes are usually in areas close to the coast or the Scottish islands. The closeness of an area to the sea has a moderating effect on temperatures in these regions, so days of frost will be less common than regions further inland.
• At a sub-regional level, some areas show an increase in the number of days of air frost, particularly in northern mainland Scotland and Orkney and Shetland.

Future climate scenarios

• The UKCIP02 scenarios report does not provide an estimate for future ground frost. However, the expected increase in minimum temperature means that the number of frosts should reduce.
• The UKCIP02 report does not mention air frost, but the reductions in expected minimum temperatures should mean some reduction in the number of air frosts also takes place.

Sea level

Key message: Scotland's sea levels may rise relative to the land, in some areas. By 2080 the current estimates range between 0 and 600 mm sea level rise.

On average, global sea levels are rising and are expected to continue to rise. However, due to changes in the level of the land, the current rate of relative sea level rise around Scotland's coastline is not uniform, with the variation being dependant on the location relative to the former centre of the Scottish ice sheet at Rannoch Moor. Closest to this centre relative sea level is currently falling whilst further away a rise of in excess of 1mm per year is being experienced. Figure 6.4 in the recent report by FRS, SEPA and SNH, "Scotland's Seas: Towards Understanding their State" illustrates this (see www.scotland.gov.uk/Publications/2008/04/03093608/0).

For Scotland, future relative sea level rise will depend on whether the rate of climate driven sea level rise exceeds the rate of falling land levels. In the current UKCIP02 estimates, the high emissions scenario predicts a relative sea level rise of around 600mm for Scotland by 2080. For the low emissions scenarios the relative rate of sea level rise is much lower and in some areas relative sea levels may continue to fall by 2080s.

Earlier estimates ( UKCIP02) included conservative factors (relating to vertical changes in land levels and global sea level rise estimates), which may have led to an underestimation of relative sea level rise. Modellers undertaking the forthcoming next generation of UKCIP scenarios are aware of these issues and will outline relative sea level rise estimates for the coming century when they publish the UKCIP08 scenarios in late 2008.

The Scottish Government has recently commissioned a report on coastal flooding, which includes updated information on sea level rise (project UKFRM10: Coastal Flooding in Scotland: A Scoping Study) which will be released September 2008. Further details can be found at http://www.sniffer.org.uk/rise.

Further information on sea level rise or average surface temperature can be found at the following links:

The National Climate Information Centre (Met Office): www.metoffice.gov.uk/climate/uk/seriesstatistics/scottemp.txt

The Scottish Government's environment statistics web pages at: www.scotland.gov.uk/Topics/Statistics/Browse/Environment

The Permanent Service for Mean Sea Level ( PSMSL), based at the Proudman Oceanographic Laboratory ( POL):
www.pol.ac.uk/psmsl

Marine Climate Change Impacts Programme annual report card available at: http://www.mccip.org.uk/arc/2007/PDF/ARC2007.pdf