Scottish Natural Capital Accounts: 2020

6. Regulating services

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:

• carbon sequestration
• air pollution removal
• noise mitigation
• urban cooling

The pollutants covered in air pollution removal are:

• PM2.5
• PM10
• nitrogen dioxide (NO2)
• ground-level ozone (O3)
• ammonia (NH3)
• sulphur dioxide (SO2)

PM2.5 is a component of PM10.

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.

Annual value of removing one tonne of air pollutant and carbon dioxide equivalent, Scotland, 2007 to 2017 Source: Office for National Statistics, Centre for Ecology and Hydrology and National Emissions Inventory

Green and blue areas in Scotland's urban areas can help reduce the temperature on hot days, leading to savings in productivity, as well as reduce noise disturbance. Regulating services, such as carbon sequestration and air pollution removal, are cross-cutting ecosystem services, provided by a range of habitats, although woodlands is the primary supplier. Analysis of these services are spoken about in more depth in the following sections.

In 2017, Scotland made up 25% of the UK's total regulating service value, with carbon sequestration in Scotland making up 40% of the UK's total value.

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. Furthermore, peatlands, which are a significant source of emissions, are only partially seen in the data.

A 2019 report by the Centre for Ecology and Hydrology (CEH) for the Department for Business, Energy and Industrial Strategy, estimates that large annual emissions for peat under forestry. This difference represents a crucial area of uncertainty in the UK emissions estimates.

The 2019 Greenhouse Gas Inventory-adjusted forest management assumptions to match the latest data on the age distribution of forests and reported wood production. This introduced an observable discontinuity in forestland sequestration for 2011 and years immediately after. This is being refined to reduce the size of the discontinuity.

For more information on the challenges and data gaps please see the Methodology guide.

Natural capital accounts based only on nature free from human intervention would include sequestration from ancient woodland but may exclude plantation forests. Human-driven emissions from damaged green spaces, such as parks, would not be included but emissions from a volcano would.

Another view of natural capital would state that all-natural habitats are somewhat modified. Usually human intervention is needed to capture value and so valuing many natural services (notably renewable energy) as if they were separate from human action is impossible. Under a human management of nature perspective, sequestration from plantation forest and emissions from degraded peatland should be included.

This is an area of research to consider further as our accounts develop. In this report we continue to use gross carbon sequestration as the asset value but present analysis of the net value to provide a rounded picture. The annual flow of the two approaches can be compared in Figure 26.

Looking only at sequestration, 11.4 million tonnes of carbon dioxide equivalent was sequestered by Scottish nature in 2017, 41% of UK gross carbon sequestration (28.0 million tonnes). This provided a £757 million service in 2017, with an asset value worth £41.7 billion, being the value of carbon sequestration by nature into the future. However, this excludes the emission costs related to the management of natural habitats.

Carbon sequestration, Scotland, 1998 to 2017

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

If we look at sequestration on a net basis, including emissions, 5.9 million tonnes of carbon dioxide equivalent was removed by nature in Scotland during 2017. Scottish forests removed 7.9 million tonnes of carbon in 2017 but croplands emitted 4.8 million tonnes. This means, whilst Scottish forests provided a £526 million service in 2017, Scottish croplands had emissions valued at negative £318 million.

This could be seen as a hidden cost of food production and, in principle, could be netted off with market-based costs such as fertiliser and fuel within the agricultural biomass account.

Net carbon sequestration by broad habitat, Scotland, 2017

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

Scottish net carbon sequestration from land use was greatest in 2017, with 20% more carbon removed than 10 years earlier. Whilst forestland continues to be the largest source of carbon sequestration, increasing net sequestration was largely caused by declining cropland emissions and increasing grassland sequestration.

Net carbon sequestration by country, UK, 1998 to 2017

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

Overall net carbon sequestration in the UK was 15.1 million tonnes in 2017. By country, 52% of net carbon sequestration was from England, 39% from Scotland, 5% from Wales, and 4% from Northern Ireland. Per hectare, Scotland has the highest net carbon sequestration at 0.74 tonnes because it has the greatest forest cover. Woodland and forest currently cover about 18.5% of Scottish land area.

Carbon removed per hectare by 'Forest land, Grassland, Wetlands, and Cropland' by local authority district areas

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

Relative to its size, South Ayrshire sequesters the most carbon in Scotland, at 2.25 tonnes of CO2 per hectare in 2017. This is because of the contribution of forestland in South Ayrshire, sequestering 318,000 tonnes, whilst croplands emitted 99,000 tonnes. Compared with other high sequestration rate areas across the UK, South Ayrshire sequesters less per hectare only than Guildford and Northumberland.

In 2017, West Lothian was the highest emitter of CO2 equivalent per hectare in Scotland at 0.46 tonnes. Whilst grasslands in West Lothian contributed 0.90 tonnes of sequestration per hectare croplands emitted 1.40 tonnes.

Largely because of the vast area covered, the Scottish Highlands contributed 13% of UK net carbon sequestration in 2017. The Highlands have slightly higher carbon sequestration per hectare than the UK average, 0.77 tonnes per hectare compared with 0.64 tonnes, and represent 11% of the area of the UK.

Covering larger areas, with generally higher than the UK average carbon sequestration per hectare, Scottish councils represent 9 out of 10 of the highest sequestering areas in the UK.

Overall, increases in net carbon sequestration and carbon prices resulted in a 38.7% rise in the annual valuation from £282 million to £392 million between 2007 and 2017. This represented 39% of the UK net carbon sequestration value in 2017 (£999 million). Excluding any carbon emissions from the management of nature, the carbon sequestration valuation of Scotland was £757 million in 2017.

Air pollution removal by vegetation

In 2017, vegetation in Scotland removed 400,000 tonnes of pollutants, which equated to a saving of £72.4 million in associated healthcare costs

Vegetation in woodland, semi-natural grassland and coastal margins all remove 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.

Total vegetation in Scotland removed almost 400,000 tonnes of PM10, SO2, NO, NH3 and O3 (excludes PM2.5 as a subset of PM10). Ground-level ozone (O3) represented the majority of total pollution removal (93%) in 2017 shown in Figure 30. PM10 is the second-largest pollutant removed, closely followed by NH3. Scotland removed 30% of the total air pollution in the UK during 2017.

Pollution removal, Scotland, 2007 to 2017

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

Notes:

1. PM2.5 is a component of PM10.

Out of the pollutants, PM2.5 is the most harmful. In Scotland the local authority level that removed the most PM2.5 per hectare was South Ayrshire (1.62 kilograms per hectare), closely followed by Dumfries and Galloway (1.59 kilograms per hectare). Despite this, these areas do not feature in the top areas that benefit from the removal of air pollution and this is because these areas have low population densities compared with the city regions.

PM2.5 removed by habitat, Scotland, 2017

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

It is estimated that in 2017, 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 £72.4 million. Although the removal of PM2.5 represents only 1.6% of total pollution removed, nearly 90% of the avoided health impacts as a result of reductions in PM2.5 concentrations are removed primarily by woodland (see Figure 32).

Avoided health costs from the removal of pollutants, Scotland, 2017

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

Most of the health benefits from air pollution removal in Scotland was in the form of avoided life years lost, with 1,549 avoided life years lost in 2017, equating to an avoided value of £67.54 million. This makes up 92% of the total Scottish annual value in 2017.

Table 2: The greatest value comes from the number of avoided years of life lost

Health impacts avoided because of the removal of air pollution by vegetation, Scotland, 2017

Pollutant	Avoided Impacts	Count	Annual value (£ million, 2018 prices)
PM2.5	Respiratory hospital admissions	33	0.28
	Cardiovascular hospital admissions	29	0.25
	Life years lost	1,481	64.61
SO2	Respiratory hospital admissions	7	0.06
NO2	Respiratory hospital admissions	8	0.04
	Cardiovascular hospital admissions	5	0.04
	Life years lost	67	2.93
O3	Respiratory hospital admissions	408	3.45
	Cardiovascular hospital admissions	68	0.58
	Deaths	174	1.31
All combined	Respiratory hospital admissions	456	3.83
	Cardiovascular hospital admissions	101	0.88
	Life years lost	1,549	67.54
	Deaths	174	1.31
	Total	2,280	73.56

Source: Office for National Statistics and 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 2017. This is because of the way the annual value estimates are calculated, which look at the total impact on health relating to the size of the population.

Avoided health costs from the removal of pollutants, Scotland, 2017

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

The present long-term asset value over a 100-year period, with income uplift and population growth, is £2.3 billion in 2017 (2018 prices), which makes up about 5% of the UK's total (£43.4 billion).

Noise mitigation by vegetation

One million people in Scotland are exposed to regular noise of 55 decibels or greater (Scottish Government), around the volume of normal speech. Vegetation acts as a buffer against noise pollution, such as road traffic noise. Noise pollution causes adverse health outcomes through lack of sleep and annoyance. 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 lower than estimates for other countries but this could be largely driven by the different noise metric used^[1]. Where these metrics were compared, the metrics used in Scotland covered a smaller area than the metric used elsewhere.

To illustrate the potential underestimate: 7,000 buildings are predicted to benefit from noise mitigation in Scotland while 12,000 are predicted to benefit in Wales. For further methodological information please see the scoping study produced by Eftec and others (2018).

Table 3: 7,000 buildings benefitted from noise reduction because of urban vegetation in Scotland

Number of buildings where road noise levels are mitigated by natural capital in Scotland

Noise band by decibel	Number of buildings benefiting from noise mitigation by urban vegetation 2 (rounded to the nearest thousand)
	England	Scotland	Wales	Northern Ireland	UK
More than 80	-	-	-	-
75.0-79.9	1,000	-	-	-
70.0-74.9	8,000	-	1,000	-
65.0-69.9	36,000	1,000	3,000	1,000
60.0-64.9	98,000	6,000	8,000	4,000
Total	143,000	7,000	12,000	5,000	167,000

Source: Eftec and others (2018)

Notes:

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

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

In 2017, the value of noise reduction in Scotland was £613,000 in avoided loss of quality adjusted life years (QALY) from sleep disturbance and annoyance. Valuations based on QALY are economic welfare values, which look in to how noise reduction affects people's social welfare.

The annual avoided loss of quality adjusted life for the UK was worth £15.3 million in 2017.

Table 4: Noise mitigation from natural capital led to a saving of £613,000 in avoided loss of quality adjusted years associated with a loss of amenity and adverse health outcomes in Scotland

Monetary accounts for the noise mitigation of urban natural capital, UK, 2017

Noise Band by decibel	Annual value of noise mitigation of 1dBA (£ thousand, 2018 prices)
	England	Scotland	Wales	Northern Ireland	UK
More than 80	1	-	-	-	1
75.0-79.9	148	-	11	2	161
70.0-74.9	1,104	8	106	56	1,274
65.0-69.9	4,026	124	313	141	4,604
60.0-64.9	7,778	481	672	324	9,255
Total	13,057	613	1,102	523	15,295

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 £33 million in 2017. Scotland made up around 4% of the £833 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 throughout this section refers to any days equal to or between 28 degrees Celsius and 35 degrees Celsius.

As shown in Figure 34, the cooling effect in both Glasgow and Edinburgh is similar, with Edinburgh's green 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 34 shows Edinburgh has a cooling effect 0.14 degrees Celsius greater than the average of the 11 Great Britain 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, 2014 to 2018

Source: Eftec and others (2018)

It should be noted that conservative estimates of the cooling effects were chosen because of the relatively simple modelling approach. This means the cooling effect of blue spaces is likely underestimated. Furthermore, the approach does not account for the cooling effects on a local level, such as shading by street trees. For more information on all the caveats, please see the scoping study by Eftec and others (2018).

Table 5 shows the value of green space in avoided labour productivity losses and air-conditioning energy costs. Urban green space in Edinburgh and Glasgow prevented costs of £560,000 during the partial hot day in 2016. This value is low compared with other Great Britain city regions such as London, which had the highest avoided costs at £237.1 million. This is because London has the largest economy and had 8.2 hot days in 2016 (see Table 5).

"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.

Table 5 also shows that in 2017 the number of hot days decreased to zero in Scottish city regions. This means that avoided costs also decreased to £0. 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).

There was a large 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. This resulted in increased avoided costs for Scotland to £3.15 million from the £560,000 seen in 2016.

Table 5: The number of hot days for the Scottish regions increased from 0 days in 2017 to 1.5 days in 2018

Number of hot days in each of the 11 Great British regions

City Region	Number of Hot Days
	2016	2017	2018
Cardiff	1.3	3.1	5.0
Edinburgh	0.2	0.0	0.5
Glasgow	0.2	0.0	1.0
Greater Manchester	1.0	0.9	4.3
Liverpool	1.0	2.2	6.2
London	8.2	7.4	22.9
North East	0.4	0.0	0.1
Sheffield	2.4	1.9	5.7
West Midlands	2.8	4.6	10.6
West of England	1.6	4.6	8.5
West Yorkshire	1.1	1.0	2.8
Scottish Total	0.4	0.0	1.5
Total	20.2	25.7	67.6

Source: Eftec and others (2018) and Met Office

Table 6: Edinburgh and Glasgow had a total avoided cost from urban cooling of £3.15 million in 2018

Total annual value of cooling from green/blue space in each of Great Britain's regions (£ thousand, 2018 prices)

City Region	Avoided Costs
	2016	2017	2018
Cardiff	£3,370	£5,260	£4,150
Edinburgh	£230	-	£380
Glasgow	£330	-	£2,770
Greater Manchester	£7,820	£1,440	£9,300
Liverpool	£4,230	£860	£4,560
London	£237,050	£207,830	£586,860
North East	£350	£40	£60
Sheffield	£3,460	£3,180	£8,210
West Midlands	£12,640	£16,080	£26,490
West of England	£4,650	£11,370	£9,530
West Yorkshire	£4,710	£1,770	£7,530
Scottish Total	£560	-	£3,150
Total	£278,840	£247,830	£659,840

Source: Eftec and others (2018) and Met Office

In Scotland, hot days are projected to increase as summer months are predicted to become up to 4.8 degrees Celsius warmer by the 2070s according to the Met Office UK Climate Projections. In England, summer temperatures have been estimated to be up to 5.8 degrees Celsius warmer. These estimations are based from a high greenhouse gas emission scenario; under lower emissions summer months could be 2.8 and 3.3 degrees Celsius warmer in Scotland and England.

Figure 35 shows the asset value of urban cooling for Glasgow and Edinburgh city regions. 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.

The asset value of the two Scottish regions combined increased marginally between 2016 and 2017 from £60 million to £64 million. The asset value for Scotland increased to a much larger extent in 2018, driven by an increase in hot days. This increase can be seen in Glasgow, having an average number of 0.10 hot days in the period 2013 to 2017, which more than doubled to an average of 0.28 in the period 2014 to 2018.

Urban cooling asset value by Scottish city region, 2016 to 2018

Source: Eftec and others (2018)