Throughout history, many scholars have tried explaining the causes of war. Thucydides, an Athenian historian, argued that war is caused when a traditional great power feels threatened by the emergence of a new rival power, whilst Clausewitz, the foremost military theorist, asserted that war is caused by a states’ pursuit of national interests. But looking at this from a different perspective, can climate change explain how war is initiated? Experts say it can.
At first sight, climate change seems unrelated to war or national security. However, security experts put increasing focus on the correlation between them. In 2014, the United States (US) Department of Defense issued a report, the Quadrennial Defense Review 2014, which acknowledges the impact of climate change on US national security, referring to climate change pressures as “threat multipliers” (p.8) that will intensify terrorist activity and other forms of violence.  Furthermore, a 2014 report by the CNA Military Advisory Board announced that extreme weather increases regional insecurities in Africa, Asia, and the Middle East; the authors suggested that climate change will be not just a multiplier, but a catalyst for instability and conflict.  The 2015 UK National Security Strategy and Strategic Defence and Security Review also identified global warming as a driver of political instability and conflict, even enhancing the likelihood of these occurring. 
One may wonder what the supporting arguments are for the alleged link between climate change and war, or how extreme weather leads to violence and instability. Colin P. Kelly, a climate scientist, explained how a severe drought in the Fertile Crescent region in the Middle East in the late 2000s contributed to the start of the Syrian Civil War.  From 2006 to 2008, the Fertile Crescent, which encompasses Syria, Southern Turkey, Northern Iraq and Western Iran, faced an unprecedented level of drought as a result of increasing temperatures and decreasing precipitations. Kelly asserted that the drought led to the collapse of agriculture in rural Syria and mass migration from rural to urban areas; this urbanisation was followed by worsened unemployment, corruption, and inequality in Syrian cities such as Aleppo, Damascus, and Deir ez-Zour, fuelling civil unrest against the government. In short, according to Kelly, extreme weather conditions had social implications, such as increasing unemployment and poverty, ultimately leading to violent conflict.
Scientists specialising in water and food security also support the suggested correlation between the drought and the Syrian Civil War. Peter H. Gleick, an environmental scientist studying water resource issues, argues that droughts and consequently failure of water distribution in Syria was followed by agricultural failure, economic dislocation, and population displacement.  This deterioration of social structure drove a massive mobilisation of political dissent and violence. On the other hand, Brent Eng and José Ciro Martinez looked at how food played a role in the Syrian Civil War and determined that a lack of food supplies and rising food prices fuelled political dissent and drove the civil rebellion against the Al-Assad regime; at the root of these water and food insecurities was drought caused by increasing temperatures and decreasing rainfall.  Therefore, it can be argued that extreme weather conditions in Syria during the late 2000s should be considered when exploring how and why the Syrian Civil War began.
These types of issues have not been limited to the Syrian Civil War. Solomon Hsiang’s quantitative analysis on the relationship between climate change and conflict, conducted across all regions of the world, produced statistical evidence that extreme weather and human conflict is correlated.  According to Hsiang, deviations from normal precipitation or mild temperature substantially increase the risk of conflict, especially in the Global Tropics. For example, in Africa, the risk of civil-war-related incidences increased by 40% when the temperature deviated by one Celsius from normal.
In support of Hsiang’s findings, there are other countries where climate is related to conflict. For example, it has been claimed that increasing violence and conflict in the Sahel countries, such as Mali, Nigeria, Chad, and Sudan, was triggered by erratic rainfall and increasing temperatures. In the Sahel region, the majority of the households depend on raising livestock for a living, but extreme weather decreases the amount of land that can be used for this.  As a result, violence is more likely because pastoralists end up competing for fertile land. As people cannot sustain their livelihoods, political dissent grows and political stability significantly decreases. People who fail to obtain fertile land and are excluded from society may end up joining organised crime or terrorist organisations, and trafficking drugs and weapons. The 2019 Adelphi Research ‘Shoring Up Stability’ report accurately illustrates this point; their two-year study conducted in the Lake Chad region of Africa concluded that climate change aggravates political and economic dislocation and undermines efforts to end conflict.  It referred to the current conflict in the region as a ‘conflict trap’ and claimed that breaking this trap requires tackling the impact of climate change.
As illustrated in the examples above, there is more than one way that climate change can affect security. The various impacts of climate change are summarised well in a report commissioned by members of the G7 group of nations – ‘A New Climate for Peace: Taking Action on Climate and Fragility Risks’ – which suggests that there are seven different ways that climate change may harm peace: (1) local resource competition; (2) volatile food prices and provision; (3) transboundary water management; (4) livelihood insecurity and migration; (5) extreme weather events and disasters; (6) sea-level rise and coastal degradation; and (7) unintended effects of climate policies. 
Research does not claim that climate change is the primary cause of conflict and war, however. Scientists Kelly, Gleick, and Hsiang all agree that war is caused by various intertwined factors, of which climate change is not the sole cause, but just one of various contributing factors. Jan Selby and Mike Hulme have criticised Kelly and Gleick’s theories, arguing that there are other significant factors that caused migration and the Syrian Civil War.  Selby pointed out that the drought not only affected Syria but other regions as well, with Syria being the only place where war was initiated, confirming that there must be other factors at play. Furthermore, he argued that rural exodus was also caused by factors other than climate change, including the privatisation of state farms, trade liberalisation, and the removal of key government initiatives like fertiliser subsidies. Lastly, poor governance was suggested as another important factor by Selby as well as Kelly and Gleick; they all noted that the Bashar al-Assad regime was extremely incapable of dealing with climate change and drought, and this further exacerbated the crisis. Therefore, it would be misleading to say climate change was the sole cause of the civil unrest in Syria.
Nonetheless, climate change is a contributing factor to violence and conflict, even though its significance may be disputable. Even Selby and Hulme, the strongest critics of this theory, acknowledge that the drought in the Fertile Crescent did contribute to migration. Even though sufficiently strong evidence to evaluate exactly how much climate change contributes to violence is lacking, it should be noted that this area of research is only in its infancy, and more research might well provide a much stronger link between the two. Given that climate change is one of the greatest challenges the world faces today and might also have a significant deteriorating effect on global security, the proposed correlation between climate change and national security should not be overlooked. Understanding this correlation may lead us to new ways of looking at regional security problems as well as a new set of solutions. This will help us think outside an existing security-focused theoretical framework about conflict and provide further insight into what else is behind it and whether this might be climate change.
Ju-Hyun is a second year BA War Studies student at King’s College London and currently studying abroad at Georgetown University in Washington, D.C. Her particular interests lie in international security not only in a military sense but also in a global health sense.
 U.S. Department of Defense, Quadrennial Defense Review 2014, Washington, DC: U.S. Department of Defense, 2014. https://archive.defense.gov/pubs/2014_Quadrennial_Defense_Review.pdf (accessed Jan 1, 2020)
 CNA Military Advisory Board, National Security and the Accelerating Risks of Climate Change, Alexandria, VA: CNA Corporation, 2014. https://www.cna.org/cna_files/pdf/MAB_5-8-14.pdf (accessed Jan 1, 2020)
 U.K., HM Government, National Security Strategy and Strategic Defence and Security Review 2015: A Secure and Prosperous United Kingdom, U.K.: the Williams Lea Group, 2015. https://www.gov.uk/government/publications/national-security-strategy-and-strategic-defence-and-security-review-2015 (accessed Jan 1, 2020)
 Kelley, Colin P., Shahrzad Mohtadi, Mark A. Cane, Richard Seager, and Yochanan Kushnir. “Climate change in the Fertile Crescent and implications of the recent Syrian drought.”, PNAS 112, no.11 (March 17, 2015): 3241-3246 https://doi.org/10.1073/pnas.1421533112
 Gleick, Peter H. “Water, Drought, Climate Change, and Conflict in Syria.” Weather, Climate, and Society 6, no. 3 (2014): 331-40. https://www.jstor.org/stable/24907379.
 Eng, Brent, and José Ciro Martinez. “Starvation, Submission and Survival: Syria’s War Through the Prism of Food.” Middle East Report, no. 273 (2014): 28-32. https://www.jstor.org/stable/24426601.
 Hsiang, Solomon M., Marshall Burke, Edward Miguel. “Quantifying the Influence of Climate on Human Conflict.” Science 341, 1235367 (2013). https://doi.org/10.1126/science.1235367
 ECOWAS and SWAC/OECD, Livestock and regional market in the Sahel and West Africa. Potentials and challenges, Paris: SWAC/OECD, 2008. https://www.oecd.org/swac/publications/41848366.pdf. (accessed Jan 1, 2020)
 Vivekananda, Janani et al., Shoring Up Stability: Addressing Climate & Fragility Risks in the Lake Chad Region, Berlin: Adelphi, 2009. https://shoring-up-stability.org/wp-content/uploads/2019/06/Shoring-up-Stability.pdf (accessed Jan 1, 2020)
 Ruettinger, Lukas, et al. A New Climate for Peace: Taking Action on Climate and Fragility Risks: An Independent Report Commissioned by the G7 Members. Berlin/London/Washington/Paris: Adelphi, 2015. https://www.newclimateforpeace.org/ (accessed Jan 1, 2020)
 Selby, Jan, Omar S. Dahi, Christiane Fröhlich, Mike Hulme, “Climate change and the Syrian civil war revisited.”, Political Geography 60, (2017): 232-244 https://doi.org/10.1016/j.polgeo.2017.05.007.