Diabetes and climate change: breaking the vicious cycle

The term ‘climate change’ refers to the longterm shift in average weather patterns worldwide. During the 11,000 years before the Industrial Revolution in the mid19th century, average temperatures across the world were stable at around 14°C. As a result of the burning of fossil fuels, humans have contributed significantly to the release of greenhouse gases, resulting in a rise in average global temperatures of around 1°C, and longterm changes to the climate. This increase has been associated with various consequences for the planet, including the acidification of oceans, soil degradation, decreased productivity of agriculture, ecosystem degradation, decreased freshwater resources, ozone layer depletion, desertification and reduced biodiversity.1 Not only does climate change have environmental consequences, but it also affects human life and health through a variety of ways. Extreme weather events and disasters threaten food security through crop destruction, as well as creating population insecurity, conflict and migration. The Intergovernmental Panel on Climate Change (IPCC) has concluded that anthropogenic effects on the climate are significant and no longer a question of scientific debate.2 The World Health Organization (WHO) suggests that over the last 30 years, climate change has resulted in an additional 150,000 deaths annually, and it estimated that between 2030 and 2050, climate change will cause approximately 250,000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress.3 Climate change is widely recognised as the single biggest health threat facing humanity, and health professionals in many parts of the world are already responding to the health harms caused by global heating. It affects the fundamental determinants of health such as access to clean air, safe drinking water, sufficient food and secure shelter. The direct damage cost to health is likely underestimated at $2– 4 billion per year by 2030. Developing countries are the most likely to be affected by climate change, and the least able to respond. The IPCC has concluded that to in order to limit catastrophic health impacts and prevent millions of climate changerelated deaths, the world must limit global temperature rise to 1.5°C.2 The climate crisis threatens to reverse the last 50 years of progress in health improvement and poverty reduction. WHO suggests that climate change is already impacting health in many ways, such as leading to death and illness from increasingly frequent extreme Received: 15 August 2022 | Accepted: 7 October 2022 DOI: 10.1111/dme.14971


| INTRODUCTION
The term 'climate change' refers to the long-term shift in average weather patterns worldwide. During the 11,000 years before the Industrial Revolution in the mid-19th century, average temperatures across the world were stable at around 14°C. As a result of the burning of fossil fuels, humans have contributed significantly to the release of greenhouse gases, resulting in a rise in average global temperatures of around 1°C, and long-term changes to the climate. This increase has been associated with various consequences for the planet, including the acidification of oceans, soil degradation, decreased productivity of agriculture, ecosystem degradation, decreased freshwater resources, ozone layer depletion, desertification and reduced biodiversity. 1 Not only does climate change have environmental consequences, but it also affects human life and health through a variety of ways. Extreme weather events and disasters threaten food security through crop destruction, as well as creating population insecurity, conflict and migration. The Intergovernmental Panel on Climate Change (IPCC) has concluded that anthropogenic effects on the climate are significant and no longer a question of scientific debate. 2 The World Health Organization (WHO) suggests that over the last 30 years, climate change has resulted in an additional 150,000 deaths annually, and it estimated that between 2030 and 2050, climate change will cause approximately 250,000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress. 3 Climate change is widely recognised as the single biggest health threat facing humanity, and health professionals in many parts of the world are already responding to the health harms caused by global heating. It affects the fundamental determinants of health such as access to clean air, safe drinking water, sufficient food and secure shelter. The direct damage cost to health is likely underestimated at $2-4 billion per year by 2030. Developing countries are the most likely to be affected by climate change, and the least able to respond.
The IPCC has concluded that to in order to limit catastrophic health impacts and prevent millions of climate change-related deaths, the world must limit global temperature rise to 1.5°C. 2 The climate crisis threatens to reverse the last 50 years of progress in health improvement and poverty reduction. WHO suggests that climate change is already impacting health in many ways, such as leading to death and illness from increasingly frequent extreme weather events, disruption of food systems and increases in food-, water-and vector-borne infections. Climatesensitive health risks are disproportionately felt by the most vulnerable, including women, children, ethnic minorities, poor communities, migrants, older populations and those with underlying health conditions. 3 Diabetes mellitus is one of the most rapidly growing diseases in the world, with its prevalence doubling in the last 20 years, with an estimated 693 million adults worldwide affected by 2045 (a greater than 50% increase from 2017). 4 The threat of climate change is directly parallel to that of diabetes. The changing climate may exacerbate health problems, worsening the morbidity and mortality of common non-communicable diseases. 5 Both diabetes and climate change are global crises with widespread intergenerational effects on health and well-being; not only do diabetes and climate change directly impact one another, but they are also both driven by similar global vectors, including rapid urbanisation, sedentary behaviour and unhealthy eating habits. Therefore, they may share common solutions.
The aim of this article is to explore the interrelationships, direct and indirect, between climate change and diabetes, the potential effects of extreme temperatures on people with diabetes, the links between diabetes and air pollution, and the role of healthcare in climate change. We also suggest some possible common solutions to climate change and the diabetes pandemic.

URBANISATION AND EXCESSIVE CONSUMPTION
Climate change and diabetes share global vectors including patterns of urbanisation, sedentary behaviour (and excessive use of transportation) and the consumption of unhealthy ultra-processed foods. Figure 1 depicts this interaction.
Urban cities are responsible for 70% of greenhouse gas emissions, 6 with cars contributing to an estimated 30% of the air pollution in cities. 7 Urban cities increase the exposure to risk factors for diabetes, especially physical inactivity-indeed every extra hour spent in a car each day increases the risk of obesity by 6%. 7 According to the United Nations (UN), over two thirds of the global population are expected to live in urban areas by 2050, 8 and accelerating urbanisation displaces agricultural land, leading to fresh produce being grown further away from the point of consumption, contributing to more carbonintensive journeys.
Urbanisation is a growing issue in low-and middleincome countries, where poor planning and uncontrolled development can lead to severe pressure on infrastructure, and a growing tide of air pollution. Furthermore, urbanisation and economic growth can also lead to greater demand for meat and cheap processed foods, which may surpass healthier diets of fresh produce and staple grains. 6 For example, meat consumption in China has quadrupled from 1980 to 2012, 9 and meat production is one of the most greenhouse gas emitting activities in agriculture (see later). Evidence from prospective cohort studies indicate that the long-term consumption of increasing amounts of red meat is associated with an increased risk of type 2 diabetes (T2D) as well as cardiovascular disease and some cancers. 10

SUPPLY
Climate change is associated with food insecurity through its ability to damage or disrupt agricultural production. It is estimated that, in the 21st century, half the world will be subject to food shortages as rising temperatures impact crops. 11 Food insecurity can create a cycle of changes, with detrimental effects on the health of individuals as well as the climate. Climate change is associated with an increased risk of fresh produce scarcity, leading to it becoming less affordable. When traditional food supplies are threatened, unhealthy ultra-processed foods which confer poor nutritional value may be more widely consumed due to their availability and affordability. 5 The increased demand for ultra-processed and imported food has a significant adverse impact on the climate, with increased greenhouse gas emissions due to their carbonintensive production, processing, transportation, retailing and storage. 6 In line with this, the increased consumption and reliance on ultra-processed food is associated with an increased risk of obesity and T2D, leading to greater ill

Keypoints
• The climate crisis and diabetes pandemic are interconnected health threats which share causes and amplify each other's health impacts. • The three shared common global vectors are increased urbanisation, increased reliance on mechanised transportation and increased production, marketing and ingestion of ultraprocessed foods. • Both crises have shared solutions, and health professionals should lead the way in acting on them.
health, and an increase in the carbon footprint of healthcare. 5 Obesity itself may increase vehicle use due to poorer mobility and lead to yet more obesity. 12 Agriculture produces a third of all greenhouse gas emissions, amounting to approximately 18 billion tonnes of carbon dioxide a year. Nitrogen oxides from fertilisers and methane from cattle are also significant sources of air pollution. 13 Livestock production is the highest greenhouse gas emitter and has a 'carbon cost' that is seven times greater than vegetables. 14 On average, meat consumption has increased from around 20 kg per annum in 1961 to 43 kg per annum in 2014, 15 and over this period, rates of obesity have doubled in most Western countries. 16 There is good evidence for an epidemiological link between obesity and excessive meat consumption, 17 as well as an increased risk for the development of T2D. 10 Dietary intervention to prevent obesity and diabetes is likely to have a positive impact on climate change. One study suggested a 61.9% reduction in the risk of developing T2D in people on a vegan diet, 51.4% risk reduction in lacto-ovovegetarians and a 38.2% risk reduction in semi-vegetarians compared to non-vegetarians. A further study suggested that if the average UK diet was optimised to achieve the WHO recommendations for nutrition, there would be an approximate 17% reduction in greenhouse gas emissions. 19 Changes in food quality may also impact on diabetes risk. Intensive agriculture has promoted yielding high quantity as opposed to high quality. Micronutrients from plant-based food come from the soil in which it is grown, but soil degradation through damaging food production methods has led to a reduction in micronutrients in many plant-based foods. 20 There is some epidemiological evidence that reduced dietary micronutrients (notably zinc, magnesium, chromium, copper, manganese, iron, selenium, vanadium, B-group vitamins and antioxidants) may reduce insulin sensitivity or secretion, and may contribute to an increased risk of T2D. 21 A further postulated mechanism by which climate change may impact on dietary risk for T2D is its impact on increased ocean temperatures. Increasing ocean temperatures have been shown to reduce marine phytoplankton, which are the primary producers of omega-3 polyunsaturated fatty acids (PUFAs). Many human diets are deficient in omega-3 PUFAs, and climate change may exacerbate this deficiency. Reduced omega-3 PUFAs are associated with an increased risk for the development of T2D. 22 In summary, climate change is likely to have a number of adverse impacts on human diets, therefore increasing the risks for development of T2D. These impacts include increasing food insecurity particularly in low-or middleincome countries, fuelling the transition from biochemically and phytochemically rich, wholesome food sources in favour of ultra-processed foods. 23 In addition, increasing consumption of meat, ultra-processed foods and reduced quality of food with loss of micronutrients is also likely to exacerbate T2D risk.

| AIR POLLUTION AND DIABETES
A complex interaction of environmental, lifestyle and genetic factors is implicated in the aetiopathogenesis of diabetes. Environmental factors such as air pollution have also been linked to the development of T2D. 24 Air pollutants may activate intracellular signalling pathways resulting in epigenetic alterations which change gene expression through DNA methylation and histone posttranslational modification. 25 Additionally, increased adipose deposition, reduced insulin sensitivity and beta cell dysfunction have all been linked to increased levels of air pollutants such as nitrogen dioxide and particulate matter with a diameter less than 2.5 μm (PM2.5). 25 Particulate matter is made up of inorganic and organic liquid and solid particles in the air, and is emitted during fuel combustion for power generation, transport and domestic heating. 26 Ammonia, nitrates, sulphates, sodium chloride, mineral dust and black carbon all contribute to the formation of PM2.5 and have been associated with adverse impacts on health. 27 Major sources of air pollution include urban traffic and biomass or industrial burning. These processes release gases such as carbon monoxide and sulphur dioxide, as well as fine particles which lead to respiratory system oxidative stress and low-grade inflammatory responses, eventually resulting in systemic inflammation and subsequently insulin resistance. 28,29 Air pollution has been linked to increased morbidity and mortality from cardiovascular and respiratory conditions, but also from diabetes. [30][31][32] The association between diabetes and with air pollution has been investigated in several studies, with most suggesting a strong association. Meta-analysis of cohort studies of 2,371,907 and 21,095 incident cases of T2D found an increased relative risk for T2D of 39% for every 10 μg/m 3 of PM2.5. 33 A further meta-analysis of 13 studies found that for every 10 μg/m 3 increase in PM2.5 or nitrogen dioxide, the risk of diabetes was increased by 10% and 8% respectively. 34 A third meta-analysis demonstrated that PM2.5 exposure and, to a lesser extent, nitrogen dioxide exposure was significantly associated with the prevalence and incidence of T2D. 35 It has also been suggested that PM2.5 could worsen glucose homoeostasis in patients already diagnosed with diabetes, 3 and excess mortality in people with T2D has been noted on days with increased air pollution.

| MEDICAL WASTE IN DIABETES
Medical devices used in the management of diabetes are frequently made of single use plastics. 36 There is increasing recognition that plastic and other waste from diabetes products is a significant and growing issue. Estimates from India in 2015 suggest that 96 million cartridges, vials and insulin pens are used each year in India alone. 37 Other potential waste from diabetes care includes glucose monitoring strips, lancets, needles, continuous glucose monitoring sensors and other material. All of the above come wrapped in plastics that are frequently not recycled. A 'Green Diabetology' movement in India is aiming to reduce plastic waste by ensuring reusable devices are used, and ensuring that all plastic is recycled. 38 Some diabetes pharmaceutical companies state they aim to recycle plastic waste, although the effectiveness of such efforts is unclear. 39

| Extreme heat
Climatic extremes can lead to adverse health outcomes among patients with diabetes for several reasons, including their increased susceptibility to heatstroke, dehydration and cardiovascular events. 40 Even short-term exposure to heat waves has been reported to lead to increased diabetes related hospitalisations, particularly among very elderly patients. A multicentre study from Brazil examined 553,351 hospitalisations, and showed a 5°C rise in mean temperature correlated with a 6% increase in diabetes hospitalisations, especially in people aged over 80 years. 41 Around 7.3% of hospitalisations were attributable to heat exposure. A study of over 4 million general practice consultations in the United Kingdom showed an odds ratio (OR) of 1.097 (95% CI 1.041-1.156) per 1°C increase in temperature above 22°C for seeking medical attention. 42 A further study of patients in Atlanta, USA, observed an association between daily maximum temperature and emergency department visits for diabetes, with the strongest associations seen in those aged 65 years and above. 43 Overall, studies investigating the association of higher temperatures with hospitalisations in people with diabetes have reported an increase ranging from 6% to 30% in the number of emergency department (ED) attendances and hospitalisations, with the largest increases seen during periods of extreme heat. 44,45 Increased mortality has also been reported with higher temperatures, with this trend being observed even in regions on different latitudes with very different climactic conditions, such as Sweden or Italy. 46 During heat waves, an approximately 56% increased risk in mortality has been seen in patients with T2D. 40 One study analysed 160,062 deaths among individuals aged over 65 in Michigan, USA and found that those with diabetes were at a higher risk of dying on hot days than those who did not have diabetes (OR: 1.17; 95% CI: 1.04-1.32). 47 A study of extreme cold and hot temperatures in two Chinese cities suggested that mortality rates would increase for around 3-7 days after an extreme cold or heat event. 48 The reasons why extreme heat adversely affects individuals with diabetes is not clear. It may be partly attributed to the effects of dehydration leading to cardiovascular events and acute kidney injury (AKI). Furthermore, polypharmacy with drugs that may exacerbate renal impairment in acute illness (angiotensin converting enzyme inhibitors, angiotensin receptor blockers, metformin, sodium glucose transporter-2 inhibitors) are more commonly co-prescribed in people with T2D. Increased risk of diabetes emergencies due to severe dehydration may also be a factor.
Autonomic dysfunction in people with diabetes has been postulated as a significant contributor. People with diabetes are more likely to experience impaired orthostatic responses in high temperatures that result in impaired thermoregulation. 49 With increasing temperature, the hypothalamus enhances sweating and increases blood flow to the skin via sympathetic nervous system activation to assist in heat loss. The gradient for dry heat exchanges between the skin and the surrounding environment increases with increased blood flow to the skin due to vasodilation. 50 Cholinergic nerves activate sweating, with the sweat then evaporating, thus cooling the body [S51]. In people with diabetes, reduced skin blood flow has been demonstrated in response to local and whole-body heating compared to healthy controls, with decreased capacity for dry heat exchange [S52], possibly due to lower nitric oxide levels and therefore less capacity for vasodilation in response to heat. In addition, the presence of atherosclerotic plaques can reduce the bioavailability of nitric oxide [S53, S54]. People with diabetes may also have an impaired sweat response, reducing their capacity for evaporative heat loss [S54]. Anhidrotic responses or hypoactive sweating are noted to be more pronounced in the lower body, with hyperactive sweating seen on the upper body [S55]. Hypoactive sweating in the lower body is likely due to autonomic neuropathy which tends to start peripherally and the hyperhidrosis in the upper body may be a compensatory response. This progresses to whole-body impairment over time, with a reduced sweating rate. It is suggested that long-term poorer glycaemic control, longer duration of diabetes, the presence and severity of neuropathy and cardiovascular fitness are factors that determine the progression of sweating impairment [S56]. Even people with good glucose control display compromised ability to regulate body temperature in heat stress. Moreover, commonly prescribed drugs such as anticholinergics, antipsychotics and antidepressants may all affect the sweating process, exacerbating heat-related risks in people with diabetes.
Mean body temperature is a composite of the skin temperature and core temperature and can be used to measure the severity of hyperthermia. Once mean body temperature reaches a certain threshold, heat loss is activated. Once maximum levels of heat loss have been reached, even if the mean body temperature increases further, no further heat loss can take place. In people with diabetes, there may be an increased threshold for heat loss as well as a reduction in the maximum capacity for heat loss and lower thermo-sensitivity levels. In the event of exposure to extreme heat, therefore, people with diabetes will demonstrate greater increases in their mean body temperature [S57, S58].
Hyperglycaemia has been demonstrated to be more common in both people with and without diabetes at warmer temperatures. This is possibly due to redistribution in blood flow between visceral and cutaneous vascular beds [S59]. Furthermore, dietary change in warmer temperatures (increasing carbonated beverage or ice cream consumption) may contribute to hyperglycaemia.
Complications of diabetes may occur more frequently in higher ambient temperatures [S60]. Acute myocardial infarction (AMI) occurs more frequently in extreme temperatures. One study looking at 53,769 hospital admissions for AMI in Hong Kong from 2002 to 2011 observed an increased risk of admission during both higher and lower temperatures, with AMI hospitalisations among people with diabetes increasing once the temperature rose above 28.8°C [S61]. Several studies have found the prevalence of gestational diabetes to be higher in warmer summer months [S62].
A practical issue faced by people with diabetes is the stability of insulin preparations in high temperatures. Exposure to extreme heat for prolonged periods can change the kinetics of insulin [S63]. Unopened vials of insulin must be stored at 2-8°C and opened vials at below 30°C for a maximum of 28 days. Being able to maintain insulin at these temperatures is not always possible; for instance, refrigerator availability is a significant barrier in developing tropical countries.
To summarise, morbidity and mortality have both been shown to increase in people with diabetes during short-term periods of heat, with a combination of factors implicated, including impaired thermoregulation and sympathetic nervous system responses at higher temperatures ( Figure 2). Furthermore, for every 1°C increase in temperature, the incidence of age-adjusted diabetes increases by 0.314 per 1000, and the prevalence of glucose intolerance increases by 0.17% [S64].

| Extreme cold
Climate change is characterised by not only global heating, but also increased extreme weather, including potentially, extreme cold. There is some evidence to suggest that people with diabetes are more vulnerable to extreme cold, leading to higher morbidity and mortality [S65, S66]. People with diabetes may be more likely to be hospitalised with hypothermia, with one study reporting that such hospitalisations and ED visits were particularly more frequent in elderly women with diabetes compared to the general population [S66]. It has been noted that the frequency of cardiorespiratory symptoms, including chest pain, arrhythmias, cough and dyspnoea among patients with diabetes during cold weather is increased [S67]. People with diabetes with known cardiovascular disease (CVD) are particularly vulnerable to hospitalisation in winter [S66].
Increased mortality from AMI has been noted in people with diabetes in colder temperatures [S68-S71]. Although it has been observed that AMI admissions rose sharply among people with diabetes in both higher and lower ambient temperatures, a stronger association was displayed at lower temperatures [S72, S73]. Low temperature may also be risk factor for hypoglycaemia [S74]. Some studies have also reported a positive association between the presence of diabetes and overall cold-related mortality [S75, S76].
Seasonal variation of glucose control has been suggested in some studies, with poorer glucose control in winter months in people with type 1 diabetes (T1D) and T2D [S77, S78]. Longitudinal follow-up of Taiwanese patients with diabetes showed a negative association between ambient temperature and HbA 1c levels [S79]. For every 1°C drop in temperature, there was an increased risk of poorer glucose control (defined as glycated haemoglobin [HbA 1c ] >7.0% [53 mmol/mol]). A further study investigated seasonal variation in HbA 1c levels in US veterans over a 2-year period and found that, after controlling for regional climate, insulin use and patient characteristics, HbA 1c levels increased over the winter months then fell during spring and summer [S80]. It has also been observed that regions that experience warmer winters display less summer-winter variability in HbA 1c . An inverse relationship has been observed between monthly changes in temperature and HbA 1c levels, with levels highest in the winter and lowest in the summer [S77, S78, S80]. It is suggested that this variation may be due to seasonal changes in diet and/or exercise levels. Indeed, one study which demonstrated that HbA 1c levels were highest during the winter and lowest during the summer in children with T1D, found that their levels of physical activity were highest during the summer [S81]. Furthermore, physiological adaptation in metabolic factors, such as glucagon, free fatty acids and ketones because of seasonal variation, may contribute to hyperglycaemia in colder temperatures [S82].
When it is cold, the body maintains its normal temperature by increasing heat production as well as increasing F I G U R E 2 Flowchart summarising the potential mechanisms through which increased morbidity and mortality may arise in diabetes patients during extreme ambient warm temperatures. AKI, acute kidney injury; AMI, acute myocardial infarction. peripheral vasoconstriction to decrease heat loss [S59]. Diabetic autonomic dysfunction may lead to impaired vasoconstriction ability, increasing core temperature heat loss and increasing risk of hypothermia [S59]. In normal physiology, exposure to cold in addition to increased body energy expenditure leads to the activation of brown adipose tissue (BAT). BAT is intensely metabolically active, mainly through possessing a unique mitochondrial protein, uncoupling protein 1 (UCP-1) found on the inner mitochondrial membrane, which generates large amounts of heat when activated [S83]. BAT activation leads to increased sympathetic nervous system activation to generate heat and leads to the oxidisation of large amounts of glucose and lipids [S84]. Activation of UCP-1 leads to dissipation of the electrochemical gradient driving ATP generation, leading to non-shivering thermogenesis. This leads to fatty acid generation which in turn further activates UCP-1, leading to increased glucose uptake in skeletal muscle. People with diabetes have reduced BAT mass and activity compared to age-matched control patients without diabetes despite having higher fat mass [S85]. This is likely to be a contributory factor in their impaired ability to generate heat in colder temperatures (Figure 3). One study found that spending 10 days in a moderately cold environment (14-15°C) could lead to a significant improvement in insulin sensitivity in people with diabetes by increasing BAT mass and activity [S86]. BAT activity has been shown to be inversely associated with blood glucose and HbA 1c levels in cold exposure, regardless of body fat levels. A modest global rise in temperature may lead to reduced BAT accumulation in the general population, as it is activated by cold exposure [S85]. Further postulated mechanisms by which cold may increase vascular risk include reduced production of nitric oxide, leading to reduced vasoconstriction [S87].

| Natural disasters
'Geo-environmental diabetology' is a term used by Cook and colleagues to describe the effects of the environment on people with diabetes [S88]. The environmental effects of geological events such as natural disasters have multifactorial consequences. These include having a detrimental effect on people's access to healthcare facilities, availability of medicines, insulin pumps and glucometers [S89].
Climatic disasters, such as earthquakes, storms and floods, weaken our capacity for diabetes prevention and treatment as well as threaten to overwhelm our healthcare systems. The potentially devastating impact of natural disasters on individuals' living conditions and the resource scarcity that can result mean that the diabetes epidemic is likely to continue growing. The formation of urban slums is more likely during disasters, and they have directly F I G U R E 3 Flowchart summarising the potential mechanisms through which increased morbidity and mortality may arise in people with diabetes during extreme ambient cold temperatures. AKI, acute kidney injury; AMI, acute myocardial infarction; BAT, brown adipose tissue; CVD, cardiovascular disease; UCP1, uncoupling protein 1. been linked to a rise in obesity and diabetes risk [S90]. Additionally, the damage and destruction of infrastructure could severely impede the delivery of vital healthcare. For example, after hurricanes in the United States, many people with diabetes, were left without access to medication such as insulin, and without access to healthcare for a prolonged period [S91]. Emergency department visits for diabetes increased by 84% following Hurricane Sandy and during power outages that had occurred subsequent to it, possibly due to the lack of access to glucose monitoring and refrigerated medications as well as a change in patients' diet [S91].

SOLUTIONS?
Sustainability can be defined as a principle that aims to meet the present generation's needs without preventing the future generation from being able to meet their own needs [S92]. Making healthcare more sustainable requires finding a fine balance between patient outcomes and environmental, social and economic consequences.
The interconnections between diabetes and climate change outlined above suggest that there may be opportunities for joint mitigation (Table 1). To catalyse the shift from the current high-carbon, obesogenic environment to more active, low-carbon living, co-benefit strategies should be adopted in food policy, transport and urban planning. For three decades, the WHO 'European Healthy Cities Network', has been promoting creation of 'healthier urban settings that support the health and well-being of the people that use them'. In their 'Urban Design for Health' publication, they describe case studies of urban areas that are improving their design to aid healthier lifestyles [S93]. For example, in the city of Cork, Ireland, a number of initiatives have been developed, including building trails, so that families and adults can navigate and move around the city easily in areas with seating and play items; creating food, nature and biodiversity trails; using mobile pot plants to close streets to cars etc.
Promoting active travel to communities as well as investing in cycling and pedestrian infrastructure could make active travel a safer, more appealing and a more viable option. Not only will a shift from car use to cycling increase individuals' physical activity, thereby decreasing their risk of T2D, but it will also reduce greenhouse gas emissions and local air pollution. Imposing restrictions on vehicles in cities and limiting car speeds could act as further incentive for people to opt for active travel.
The design and layout of cities, streets and buildings can act as a barrier to physical activity and can encourage the use of motorised transport. Enforcing mixed land use, with housing, employment and retail areas interlinked by open green spaces, could have wider societal benefits. This would allow adequate space for walking and cycling within urban cities, facilitating a healthier lifestyle and reducing carbon emissions. Examples of this include the Ciclovia active travel scheme in Bogota in which 75 miles of Bogota's city streets are shut to motorists every Sunday and are handed over to cyclists, walkers and runners [S94]. It is a widely loved scheme, with a quarter of residents making use of the cycling path network every Sunday. Women who take part in the scheme regularly are seven times more likely to be physically active, proving that these measures can improve sustainability and urban health.
Facilitating a shift in diet from heavily processed and animal product-based foods to a more sustainable diet could better support healthy living and reduce carbon emissions. Prioritising local food production and supporting small scale farmers as opposed to industrial methods, can help ensure food security and green economy while protecting natural resources. Food labelling, awareness campaigns and nutritional guidance presented to the public in an easily understandable format could aid healthier eating. Urban farms, farmer markets and school gardens can assist in a shift to urban agriculture and local food production, scaling up access to local fresh and seasonal foods to urban communities and thus, reducing their reliance on easily accessible processed foods.
Heat waves cause higher morbidity and mortality in people with diabetes. Larger scale studies are needed to further our understanding of the pathophysiology underlying these consequences as well as to further explore the impact of climate change on people living with diabetes. Patients should be advised by their primary care physicians and endocrinologists to avoid extreme cold and heat and if this is not possible, they must be monitored more frequently during extreme weather. Measures need to be put in place in extreme heat events whereby vulnerable patients can stay home or have access to cooling options. Preparedness plans could help mitigate the effects of extreme weather events. For example, the Diabetes Disaster Response Coalition and Juvenile Diabetes Research Foundation have produced a joint 'patients with diabetes preparedness plan' to ensure patients have insulin, supplies and the support that they need in the event of a major storm. Additionally, 'Insulin for Life USA' have pledged free insulin and diabetes management supplies to disaster-affected countries through accepting donations of insulin, glucometers and test strips [S95].
More work also needs to be done to reduce the carbon footprint of healthcare. If global healthcare were considered a country, it would rank as the fifth biggest carbon emitter worldwide. The UK's largest public sector greenhouse gas emitter is the National Health Service [S96]. It is the responsibility of all people involved in healthcare to reduce greenhouse gas emissions and make healthcare more sustainable. Simple interventions to reduce carbon emissions include stopping the use of halogenated anaesthetic agents, reducing or stopping the use of single-use medical devices (such as insulin pens), improving waste sorting and recycling, and promoting remote consultations to reduce travel [S97].
Overconsumption, over-automation, mass food production and globalisation are all factors relied on to drive economic growth, but they also drive the global diabetes epidemic and climate change. Fundamental changes to lifestyle that require coordinated thinking and policy integration to lead to more sustainable living will be no quick fix but could enable huge change when it comes to helping avert the looming catastrophes of climate change and diabetes. Failing to anticipate and prepare for the detrimental effects of climate change as well as failing to act now to mitigate these effects and the impact these would have on diabetes could have dire consequences. These three aspects must be united in a development goals framework rooted in sustainability, equity and social justice.

| EDUCATION
As well as educating the public, there is a growing need for health professionals dealing with people living with diabetes to be educated in the potential effects of climate change on human health, and to become advocates for change. This education should commence in undergraduate training, making students aware of the co-benefits of climate change mitigation and promoting active travel and sustainable eating practices. It is also important to learn about adaptation measures to minimise harm in people with diabetes during extreme weather events. An emphasis on sustainability in public health and global health modules of health curricula would seem appropriate, but efforts to include sustainability in all aspects of the curriculum, even from the earliest years, is important [S98].
Involving health professionals in mitigating climate change in their lives and in health systems may offer some important benefits for patients and healthcare professionals. In our own trust, a special interest group called 'Green at Barts Health' aims to 'support and challenge the Trust to achieve its reduction in carbon emissions, and sustainability goals' [S99]. The group have been involved in ensuring sustainability of new hospital development projects, campaigns around clean air, educating healthcare professionals about sustainability and developing sustainability quality improvement projects.
Sustainability in diabetes is becoming increasingly recognised as an issue that needs addressing. The US-based 'Diabetes Technology Initiative' is working to highlight the issue among healthcare professionals and people living with diabetes [S100].

| CONCLUSIONS
Diabetes and climate change are interconnected. Global heating leading to increased temperatures and extreme weather events are likely to have a disproportionate effect on people living with diabetes, especially those with diabetes complications. Many people living with diabetes are reliant on regular medications for management of glucose and cardiovascular complications, and the disruption in the supply of such therapies due to extreme weather could have a major effect on people's lives. Sustainable eating • Prioritising local food production.
• Improving food labelling, awareness campaigns and nutritional guidance.
• Urban farms and farmers' markets.

Adaptation
Advice and preparedness plans • Further research to understand the impact of extreme heat and cold on people with diabetes to better advise patients. • Identify patients who may be vulnerable and offer individualised management plans. • More frequent monitoring and check-ups during extreme weather. • Measures to ensure patients can stay home when it is safer for them to do so and have access to options to keep cool or warm. • Preparedness plans for medication and support for climatic disasters.
Transition to low carbon living will not only mitigate harm from climate change, but also enhance the well-being of people living with diabetes, and potentially reduce the number of people living with the condition. National and local government should implement environmental and urban planning, and food policies to encourage healthier living, and healthcare professionals dealing with people living with diabetes need to be strong advocates for sustainability in healthcare. Time is short, and there is much to be done.