Scottish Natural Capital Accounts: 2021

4. Regulating services

ONS

As well as provisioning services, natural assets provide several less visible services known as regulating services. A regulating service is an ecosystem benefit, which moderates natural phenomena. Regulating services include cleaning the air, sequestering carbon and regulating water flows to prevent flooding.

This section presents four regulating ecosystem services:

1. Carbon sequestration

2. Air pollution removal

3. Noise mitigation

4. Urban cooling

Green and blue areas in Scotland’s urban areas can help reduce the temperature on hot days, leading to savings in productivity, and can reduce noise disturbance. The annual value of Scottish urban cooling in 2018 was £3.22 million and Scottish noise mitigation equalled £0.63 million in 2018.

Air pollution leads to respiratory diseases in humans. The risk of those diseases for a population can be estimated based on the levels of pollution and the health costs of that disease.

Both carbon sequestration and air pollution removal are carried out by vegetation. The capacity for vegetation to sequester carbon and remove air pollution changes with the amount of vegetation.

The valuation methods used differ; carbon sequestration is a removal cost, and air pollution removal is a societal cost. That is, we are measuring the value of avoiding damage (for carbon) and the value of treating existing damage (for air pollution). Air pollution removal valuation does not account for the cost of abatement, and carbon sequestration valuation does not consider the global societal impacts of carbon dioxide.

The amount of carbon sequestrated is substantially more than the amount of air pollutants removed by vegetation. However, the value per tonne of air pollutant removed is on average four times higher than a tonne of carbon removed. This is because the avoided health impacts of pollutants, mainly PM2.5, provide significant benefits to society.

In 2018, the annual values for Scottish carbon sequestration and air pollutant removal equalled £768 million and £72 million, respectively (2019 prices).

Annual value of carbon sequestration and air pollutant removal, Scotland, 2007 to 2018

Source: Office for National Statistics, National Atmospheric Emissions Inventory (NAEI), and UK Centre for Ecology and Hydrology

Carbon sequestration

When using this analysis, it is important to note that we do not capture all carbon sequestration. Because of a lack of data, values related to carbon sequestration by marine ecosystems are not included in the current estimates. Peatlands, which are a significant source of emissions, are only partially seen in the data.

A 2017 report by the UK Centre for Ecology and Hydrology (UKCEH) for the Department for Business, Energy, and Industrial Strategy (BEIS), estimates that Scotland has only 25% (or 490,497 hectares) of its total peatlands (1,947,750 hectares) in a near natural condition, which have a net cooling effect on the climate. Scottish peatlands, which make up 67% of the UK’s total peatland area, generated an estimated 41% (9,706 ktCO² equivalent) of 1990 UK emissions (23,664 ktCO² equivalent). This almost completely negates the gross terrestrial sequestration of Scotland reported in the Greenhouse Gas Inventory (GGI).

Over the time series, the amount of carbon sequestered has been fairly consistent, with 11.27 million tonnes of CO₂ equivalent being sequestered in Scotland in 2018 (Figure 22). This represents 40% of the UK total amount sequestered (28.09 million tonnes). The annual value of this ecosystem service for Scotland was valued at £786 million in 2018 (Figure 21). The asset value was £44 billion in 2018, which reflects the value of carbon sequestration by nature into the future. However, this excludes the emission costs related to the management of natural habitats.

Million tonnes of CO₂ equivalent of carbon sequestered for Scotland and UK, 1998 to 2018

Source: Office for National Statistics and National Atmospheric Emissions Inventory (NAEI)

An assessment of Scotland’s blue carbon resources (2017) estimates the scale of carbon production and storage in Scottish inshore Marine Protected Areas (MPA) and Special Areas of Conservation (equal to around 11,350 km2). Estimates show that stocks of carbon, in inshore MPAs in both living materials and sediment, are estimated to be 9.4 megatons of organic carbon and 47.8 megatons of inorganic carbon.

Annually, the living components of inshore MPA habitats are estimated to emit 248,000 tonnes of organic carbon. MPA sediments sequester 126,000 tonnes of organic carbon. This means that Scotland’s MPAs stores around half of the organic carbon it produces. However, most of the sequestered organic carbon is likely to originate from land rather than the marine environment.

Scottish MPAs production of inorganic carbon is vastly outweighed by the quantity of inorganic carbon it sequesters, by around 950% – while 36,000 tonnes of inorganic carbon are produced, 348,000 tonnes of carbon are stored each year. The major difference between inorganic carbon production and sequestration has several possible explanations. Inorganic carbon production may be underestimated, and inorganic carbon sequestration may be overestimated. Furthermore, Scottish inshore MPAs may sequester inorganic carbon that originates from outside the MPA zone.

Air pollution removal

Vegetation removes airborne pollution from the atmosphere. We can measure the benefits of this to humanity by looking at the savings to health costs associated with breathing in air pollutants. The air pollutants we measure are PM10, PM2.5, SO₂, NH₃, NO² and O³. More information on the type of health costs saved and the method of measuring this benefit can be found in the methodology section. In 2018, it is estimated that vegetation in Scotland removed 399 thousand tonnes of pollutants, representing 30% of the total air pollution removed in the UK during 2018. Ground level ozone (O³) represented 95% of all pollutants removed in 2018 (Figure 23). Woodland habitats in Scotland removed the most pollution at 111,000 tonnes (Figure 24).

Air pollution removal, thousand tonnes, Scotland, 2007 to 2018

Source: Office for National Statistics and UK Centre for Ecology and Hydrology

Out of the pollutants, PM2.5 (fine particulate matter with a diameter of less than 2.5 micrometres, or 3% of the diameter of a human hair), is the most harmful. PM2.5 can bypass the nose and throat to penetrate deep into the lungs, leading to potentially serious health effects and healthcare costs. In Scotland 83% of PM2.5 is removed by woodlands.

In Scotland, the local authority level that removed the most PM2.5 per hectare was South Ayrshire (1.59 kilograms per hectare), closely followed by Dumfries and Galloway (1.56 kilograms per hectare). Despite this, these areas do not feature in the top areas that benefit from the removal of air pollution because they have low population densities compared with the city regions.

Air pollutant removal by habitat, thousand tonnes, Scotland, 2018

Source: Office for National Statistics and UK Centre for Ecology and Hydrology

It is estimated that in 2018, the avoided health costs in the form of avoided deaths, avoided life years lost, fewer respiratory hospital admissions, and fewer cardiovascular hospital admissions, amounted to a substantial £72.1 million. Although the removal of PM2.5 represents only 1.6% of total pollution removed, 89% of the avoided health impacts are a result of reductions in PM2.5 concentrations.

Avoided health costs from the removal of pollutants, Scotland, 2018

Source: Office for National Statistics and UK Centre for Ecology and Hydrology

The two most populated areas in Scotland (Glasgow and City of Edinburgh) reported the most savings in associated health costs during 2018. This is because annual value estimates look at the total impact on health, which relates to the size of the population.

Avoided health costs from the removal of pollutants, Scottish local government councils, £ million, 2019 prices, 2018

Source: Office for National Statistics and UK Centre for Ecology and Hydrology

The present long-term asset value over a 100-year period, with income uplift and population growth, was £2.3 billion in 2018 (2019 prices).

Noise mitigation by vegetation

The Scottish Government estimated over one million people in Scotland are exposed to regular noise of 55 decibels or greater, around the volume of normal speech. Vegetation acts as a buffer against noise pollution in, for example, urban areas with road traffic noise. Forest Research identified planting buffers of trees and shrubs can reduce noise by five to ten decibels for every 30 metres width of woodland. Noise pollution causes adverse health outcomes through lack of sleep and annoyance, even hearing loss from prolonged exposure. Eftec and others (2018) have developed initial estimates of the benefits vegetation has in reducing noise.

These estimates are considered minimum values, but further work is needed to develop more refined and robust estimates. The number of buildings receiving mitigation in Scotland is estimated to be 7,000 (Table 1). This is lower than estimates for other countries but could be largely influenced by the different noise metric used. Where these metrics were compared, the metrics used in Scotland covered a smaller area than the metric used elsewhere. For further methodological information please see the scoping study produced by Eftec and others (2018).

Table 1: 7,000 buildings benefitted from noise reduction resulting from urban vegetation in Scotland

Number of buildings where road noise levels are mitigated by vegetation in Scotland (rounded to the nearest thousand)

Source: Eftec and others

Notes:

1. 5 dBA bands applied along with guidance in Defra’s noise pollution: economic analysis published in 2014.

2. Number of dwellings receiving mitigation in Scotland is likely to be lower than the estimates for the other countries because Eftec and others 2018 used the Lden noise metric rather than the LA1018 metric which was not available for Scotland.

3. Urban vegetation includes large woodlands (>3,000m²) and smaller woodlands (<3,000m²), but not very small woodlands (<=200m²).

In 2019, the value of noise reduction in Scotland was £625,000 in avoided loss of quality adjusted life years (QALY) from sleep disturbance and annoyance. Valuations based on QALY are economic welfare values, which investigate how noise reduction affects people’s social welfare. The annual avoided loss of quality adjusted life for the UK was worth £15.6 million in 2019.

Table 2: Noise mitigation from natural capital led to a saving of £625,000 in avoided loss of quality adjusted years associated with a loss of amenity and adverse health outcomes in Scotland

Annual value of noise mitigation (£ thousand, 2019 prices), UK, 2019

Source: Eftec and others (2018)

Notes:

1. 5 dBA bands applied along with guidance in Defra’s noise pollution: economic analysis published in 2014.

The asset value of noise mitigation from vegetation in Scotland was £34 million in 2019. Scotland made up around 4% of the £849 million asset value of noise mitigation across the UK. The asset value for noise reduction in Scotland is based on the estimated future flow of benefits over 100 years.

Many assumptions were made when estimating the future flow of value from noise mitigation by urban vegetation. For example, population affected was held constant and the impact of electric cars was not considered.

Urban Cooling

The urban heat island effect means that cities and towns are prone to higher temperatures than the rural environments surrounding them. Green and blue spaces, such as parks and lakes, can cool urban environments through the process of evapotranspiration and shading. This benefits the economy by avoiding labour productivity loss and reducing the use of artificial cooling (air conditioning).

Eftec and others (2018) estimated the cooling effect provided by natural capital for 11 city regions across Great Britain, including two Scottish regions – Glasgow and Edinburgh. The cooling effect is based on reducing heat on hot days. “Hot days” refers to any day with a temperature between 28 degrees Celsius and 35 degrees Celsius, as defined by the Eftec and others (2018) report.

As shown in Figure 27, the cooling effect in both Glasgow and Edinburgh is similar, with Edinburgh’s green and blue space providing just 0.08 degrees more cooling. Cooling is dominated by green spaces as opposed to blue spaces.

Edinburgh has a greater cooling effect than all other city regions mentioned in Eftec and others (2018), closely followed by Glasgow. Figure 27 shows Edinburgh has a cooling effect 0.14 degrees Celsius greater than the average of the 11 Great British city regions covered. Scottish cities have the highest cooling effects because of the amount of woodland relative to the size of the city region.

Average annual cooling effect of green space and blue space in all Great British regions, degrees Celsius, 2014 to 2018

Source: Eftec and others (2018)

The value of green space in Scotland - measured in terms of avoided health costs – was £3.22 million in 2018 (Table 4). This value is low compared with other Great British city regions such as London, which had the highest avoided costs at £599.27 million in 2018. This is because London has the largest economy and highest number of hot days (see Table 3).

There was a significant increase in the number of hot days across the UK in 2018, nearly triple what was experienced in 2017, at 68 days. Scottish city regions experienced 1.5 hot days in 2018. This resulted in increased avoided costs for Scotland to £3.22 million from the £570,000 seen in 2016 (2019 prices). Between 2016 and 2017, most of the 11 city regions saw an increase in avoided costs. Unlike Edinburgh and Glasgow, many regions had an increase in the number of hot days (five more than 2016 overall).

Source: Eftec and others (2018) and Met Office

Notes:

1. In 2017 there were no days classed at hot days in Edinburgh and Glasgow.

Source: Eftec and others (2018) and Met Office

The asset value of urban cooling for Glasgow and Edinburgh city regions are £72.4 million and £33.94 million, respectively (2019 prices). These are calculated using the average number of hot days over the last five years and projected green space urban cooling increases over the next 100 years.