Climate encompasses the averages, variability, and other statistics of weather over several decades or longer, while weather reflects short-term conditions of the atmosphere in a particular region. Weather includes very hot or cold or rainy days, while extreme weather events include extended droughts, floods, heatwaves, coldwaves, and intense tropical storms.

Climate change reflects nonrandom change in climate measured over several decades or longer.

Climate variability reflects the way that climate fluctuates above or below long-term average values. We use the terms developed and developing countries to differentiate between states that are broadly industrialized with relatively high per capita incomes and those where industrialization and wealth are more limited. For the purpose of this study, “developing countries” are those included in the IMF’s “emerging markets and developing countries” group, defined as all countries besides the advanced economies of the United States, Canada, Western Europe, Japan, South Korea, Australia, and New Zealand. Although the World Bank now uses more precise terms to characterize economic development and more organizations are likely to do so, we retain the traditional terms, given their widespread conventional use, including by the United Nations and business entities.

Globalization is the process of interaction and integration among the world’s people, companies, and governments, driven by the movement of trade, capital, people, ideas, and information across borders.

We follow World Bank researchers in defining governance as “the traditions and institutions by which authority in a country is exercised.” This includes “the process by which governments are selected, monitored, and replaced; the capacity of the government to effectively formulate and implement sound policies; and the respect of citizens and the state for the institutions that govern economic and social interactions among them.”

Internally displaced person (IDP) is a person or groups of persons who have been forced or obliged to flee or to leave their homes or places of habitual residence as a result of or in order to avoid the effects of armed conflict, situations of generalized violence, violations of human rights, or natural or manmade disasters, and who have not crossed an internationally recognized national border.

International system refers to the distribution of power and interactions among states as well the suite of institutions, rules, and norms that guide these interactions. The term international order is often used to characterize the nature of these interactions, typically associated with specific types of order such as the rules-based international order created after 1945.

Islamist describes a movement or approach dedicated to increasing the role of Islam in politics and sometimes other aspects of public life, and may or may not be violent.

Major economies are the world’s largest developed economies—the G7 member states: the United States, Japan, Germany, the UK, France, Italy, and Canada, plus China. These are not the “largest economies,” because Brazil and India have surpassed Canada and Italy in nominal terms, and several additional countries— Russia, Indonesia, Mexico, South Korea, and Saudi Arabia—supplant some G7 members in purchasing power parity terms. Nonetheless, we have used this grouping to reflect a balance of national economic size and per-capita wealth, as well as shared demographic challenges.

A migrant is any person who is moving or has moved across an international border or within a state away from his/her habitual places of residence, regardless of 1) the person’s legal status; 2) whether the movement is voluntary or involuntary; 3) the causes driving the movement are; or 4) duration of stay.

Migration is the movement of a person or a group of persons, either across an international border or within a state. Migration is a population movement, encompassing any kind of movement of people, whatever its length, composition, and causes. It includes refugees, displaced persons, economic migrants, and persons moving for other purposes, including family reunification.

Nationalism is an ideology based on the premise that an individual’s loyalty and devotion to the nation surpass other individual or group interests A nation is a large body of people united by common descent, history, culture, or language, living in a particular state or territory. A nation may or may not be a state.

Nativism is the promotion of the interests of native-born or established inhabitants against those of newcomers or immigrants and may also be expressed as an emphasis on traditional or local customs as opposed to outside influences.

Populism is a political program that champions the common person, usually in contrast to elites. Populist appeals can be from the political left, right, or combine elements of both. Populism can designate democratic and authoritarian movements and typically promotes a direct relationship between the people and political leadership.

A refugee is a person who, according to the 1951 UN Refugee Convention, “owing to a wellfounded fear of persecution for reasons of race, religion, nationality, membership of a particular social group, or political opinions, is outside the country of his or her nationality and is unable or, owing to such fear, is unwilling to avail him or herself of the protection of that country.”