Scientifically, it cannot be proven that any disaster is happening more often because of climate change. What can be proven is that these natural disasters are more intense and more destructive, due to climate change. Historically, policy and legislative change has only happened after experiencing a natural disaster of epic proportions.

Climate Change & Natural Disasters

  • The general thought process on the correlation between the climate change and natural disasters is that the conditions created by global warming can affect natural disasters. Increasing global surface temperatures increase the possibility of more droughts and storms with increased intensity. Water vapor evaporating into the atmosphere becomes “fuel” for powerful storms to develop. More heat in the atmosphere and warmer ocean surface temperatures can lead to increased wind speeds in tropical storms. They key question though, is can it be proven?
  • Disasters are unfortunately part of life. Scientists do not believe disasters are directly from climate change, but they do believe that it makes these events more likely and more severe.
  • The number of climate related disasters has tripled in the last 30 years.
  • The US has had 273 weather and climate disasters since 1980 where the overall costs exceeded $1 billion.
  • Of all the studies highlighted over the years, 65% have found that climate change increased the severity or likelihood of an event.

The Evolution of Studying Climate Change & Natural Disasters

Myles Allen- Blaming Climate Change on Individual Disasters

  • One night, in 2003, during a flooding event, Myles Allen sat in his Oxford home thinking about climate change. The predominant view of the science community at this point was that while they felt climate change affected the weather, there was no way to determine the influence it had on a singular weather event. There were too many factors affecting the weather. Allen felt differently.
  • Fifteen years later, he has made significant progress in proving that certain disasters can be correlated to climate change. He essentially started a new field of scientific study, extreme event attribution studies. In 2004, he and his colleagues authors a report that is regarded as the first extreme event attribution study. That paper examined that contribution of climate change to a European heat wave in 2003. They concluded that”it is very likely that human influence has at least doubled the risk of a heat wave exceeding this threshold magnitude.”
  • They used a climate model to compare simulations for climate change with different scenarios, including what would happen if climate change did not exist. They found that climate change roughly doubled the risk of an individual heat wave. The key to their success was not asking if it caused the event, but how much it might have affected the change of it occurring at all.

2010 Russian Heat Wave

  • In 2010 a heatwave that broke records swept across Russia. Two separate studies attempted to “quantify the influence of climate change on that event”. They came to very different conclusions.
  • One research paper suggested that the heatwave was a product of natural climate variations, while the other claimed that human caused climate change was a major factor. The main problem was that they investigated two different themes, one the severity of the event, and the other the overall probability of an event occurring.
  • While the events were contradictory, it was an important step, as scientists learned more about climate change research.

Research Today

  • Scientists generally agree that extreme attribution studies do not predict the likelihood of a future event, instead they focus on how climate change has effected events that have already happened.
  • A National Academy of Sciences report warned, “Attribution studies of individual events should not be used to draw general conclusions about the impact of climate change on extreme events as a whole.”


As with wildfires, the most consistent research focuses on how climate change affects real events, not the likelihood of an event occurring. The consensus is that storm intensity will increase, but frequency will most likely remain unchanged. We will see more precipitation, stronger winds, and a greater reach of the hurricane.

Facts & Figures

  • For every 1.8°F increase in the global temperature, there is a 7% increase in the moisture holding capacity of the atmosphere. According to the National Wildlife Federation, the warm water and air contributed to the 27 trillion gallons of rain that Hurricane Harvey delivered. Another study found that the risk from a Hurrican Katrina level storm surge rose 2-7 times for every 1.8 degree increase in temperature.
  • Sea levels are rising due to thermal expansion, melting glaciers, and the melting of polar ice caps. The rising sea levels create a “launch pad” for storm surges while also being a barrier to flood waters emptying back into the ocean.
  • It is suggested that climate change boosted Hurrican Harvey’s rainfall by 20-40%. To obtain this data, scientists compared rainfall levels with those that were predicted by a computer model that simulated the hurricane using greenhouse gas levels from more than 60 years ago.
  • The atmosphere holds 4% more water vapor than it did 40 years ago. Kevin Trenberth of the National Center for Atmospheric Research explains that “the convergence of moisture into a storm not only leads to higher precipitation but also, for certain storms, greater intensity and growth.”

Hurricane Research

  • The National Science Foundation estimates that “recent named storms would be slower-moving, have faster winds, and be much wetter, on average, if they’d formed in a climate warmed by 5 °C (9 °F)—the change predicted in average temperature over the next century. In other words, the models suggest that even devastating hurricanes such as Harvey will be worse in the future “.
  • Studies have shown there is “no discernible trend in the global number of tropical cyclones.” Part of this is due to the erratic patterns of hurricanes. This makes them hard to predict.

hurricane [patterns

  • A 2013 study found no “human-caused signal in annual global tropical cyclone or hurricane frequencies.”
  • A 2019 paper, led by scientists at NOAA’s Geophysical Fluid Dynamics Laboratory, indicate that global warming plays a role. They used simulations that provide the rapid intensification of storms it outside any expected norm and is due to climate changes.
  • A 2018 study by NOAA, The National Oceanic and Atmospheric Administration, discovered a 10% reduction in the speed of tropical cyclones since 1949. This is concerning, as this increases the amount of time that a hurricane remains on land. Hurricane Michael brought a storm surge of as much as 14 feet to areas that did not normally flood in the panhandle.
  • Tropical storm data from the last 39 years indicates “the probability of a hurricane having wind speeds of at least 100 knots increased by approximately 15% between the early and latter halves of the 39-year record.”
  • According to NOAA, 85% of all damage comes from category 3, 4, and 5 storms. In a 2015 research paper, it was found that there was an “increase in average cyclone intensity, precipitation rates, and the number and occurrence days of very intense category 4 and 5 storms.” “Specifically, the simulations calculated a 28% increase in category 4 and 5 storms globally, with a 335% increase in the northeast Pacific and a 42% increase in the North Atlantic”.

storm strength

Factors That Increase Destructive Potential of Hurricanes

  • The oceans have absorbed a 93% increase in the planet’s energy from 1971-2010.
  • Since 1970, sea surface temperatures have warmed, on average, 0.1°C per decade. These temperatures are one of the key factors that strengthen hurricane development.

hurricane intensity

  • Sea surface levels have risen roughly 7-8 inches since 1900. These higher levels give coastal storm surges a higher starting point, therefore reaching more land. “Hurricanes require high humidity, relatively constant winds at different altitudes, and can occur when surface ocean temperatures exceed about 79°F (26°C). “


The link between climate change and tornadoes is a complex one, and is currently unclear. “Current data on tornadoes is inconsistent because measuring the presence of tornadoes relies on eyewitness accounts and aftermath damage assessments rather than quantifiable data”.

Challenges in Measuring Tornadoes

  • Tornadoes are geographically small and intense, making them challenging to simulate in climate models.

Tornado Research

  • Multiple studies find that the conditions that produce the worst thunderstorms are more likely in a warmer world.
  • While the days per year with one tornado is decreasing, the days per year with more than 30 tornadoes is increasing.


  • In 2019, the US had one of their worst tornado outbreaks of the past decade, with more than 500 reported over 30 days. Even with these statistics, scientists have a low confidence in detecting a link between climate change and increased tornado activity. They are reluctant to exclude this possibility, but the science is uncertain at this point.
  • There are no observable increases in the number of strong tornadoes over the past few decades, but they have become more clustered with multiple outbreaks. There are more days in which multiple outbreaks occur, but fewer overall days with tornadoes.
  • There is evidence that the power of the tornadoes has been increasing, but this could also be based on advances in tornado reporting since the 1970s.
  • The Fourth National Climate Assessment stated, “Observed and projected future increases in certain types of extreme weather, such as heavy rainfall and extreme heat, can be directly linked to a warmer world. Other types of extreme weather, such as tornadoes, hail, and thunderstorms, are also exhibiting changes that may be related to climate change, but scientific understanding is not yet detailed enough to confidently project the direction and magnitude of future change.”

tornado research


Although there is not a direct relationship between climate change and fire, research has found strong connections between warmer temperatures and larger fire years. Climate models state that the average temperatures will increase, but ignition is the factor that remains a mystery. It is complicated, because scientists do not understand that will happen with storms and the amount of lightning they will produce.

Wildfire Background Information

  • Wildfire risk depends on various factors including temperature, soil moisture, the presence of trees and shrubs, and other fuel sources. Climate change creates these fuels, trees and shrubs for example, to be drier.
  • The number of large wildfires has doubled since 1984.
  • More than 80% of wildfires are caused by people, but the warmer temperatures help to fire to spread and make them harder to put out. Globally, it is estimated that just 4% of fires start naturally.

Wildfire Research

  • A study released this year found that climate change made the conditions for Australia’s 2019-2020 bush fires 30% more likely.
  • Even though the conditions are more likely, research found that the total area burned by wildfires has decreased by up to a quarter over the last 20 years globally. This could be attributed to changes in how we use land.
  • A 2015 study found that, globally, the number of days where wildfires were likely to burn has risen due to climate change.
  • Research conducted on Canada’s 2017 fire season found that the extreme warm and dry conditions burned 1.2 million hectares of land. They estimated that this was made 7-11 times larger due to climate change.
  • A 2020 research paper found that the number of autumn days in California with weather suitable for wildfires has doubled since the 1980s due to climate change.
  • Science Brief, a UK based website, reviewed 73 different scientific studies. They found that climate change is increasing the risk of wildfires globally. “Our main focus in the ScienceBrief review was on fire weather and how it is impacted by climate change. We found unequivocal evidence — based on observations and models spanning key global regions — that anthropogenic climate change has increased the flammability of landscape fuels and placed upwards pressure on fire activity.”
  • The 2015 Alaskan fire season burned 5.1 million acres. Researchers found that an “unusually high number of lightning strikes occurred, generated by the warmer temperatures that cause the atmosphere to create more convective systems — thunderstorms — which ultimately contributed to more burned area that year”.
  • According to Yale Climate Connections, in the western US, wildfires larger than 1,000 areas have become almost 5 times more frequent than in the 1970s.

Economic/Policy Changes Attributed to Natural Disasters

  • Overall, policy changes only come in the wake of some of the worst natural disasters. Hurricane Katrina led to a “sweeping reassessment of federal disaster policy”. Hurricane Sandy highlighted the need to improve coastal resilience.
  • Responses come in four different categories.

policy responses to natural disasters

  • The majority of policy changes deal with emergency preparedness, response, along with planning and partnership initiatives.


History of Federal Disaster Policies

  • 1947– Congress “charged the War Assets Administration and the Federal Works Agency with delivering surplus federal supplies to areas in need”.
  • 1950-1953– The Distaster Relief Act of 1950 established a permanent source of disaster relief funds.
  • 1961– The Office of Emergency Planning was charged with coordinating civil defense and disaster-related emergency efforts.
  • 1965– In response to Hurricane Betsy, the government more fully engages the Army Corp of Engineers to work with the Orleans Parish Levee Board to build levees and related works.
  • 1966– In response to the Alaska earthquake, a Midwest tornado outbreak, and Hurricane Betsy, the government amended the 1950 act to allow rural communities to participate, provide aid for damaged higher education institutions, repair public facilities under construction, and creased the office of Emergency Planning.
  • 1968– Congress creates the National Flood Insurance Program.
  • 1969– The Disaster Relief act is modified in response to Hurricane Camille, to include things such as debris removal, unemployment benefits, and loan programs.
  • 1970– The Disaster Relief Act expanded policies and put an emphasis on aiding individuals and hazard mitigation.
  • 1970sFIRESCOPE is initiated in Southern California. Firecope stood for Firefighting Resources of Southern California Organized for Potential Emergencies and they set out to develop two interrelated, yet independent, systems for managing wildland fire. They created the Multiagency Coordination System (MACS) and the Incident Command System (ICS). Congress allocated $900,000 to the US Forest Service to develop these systems.
  • 1974– In response to Hurricane Agnes, the definition of a major disaster is redefined to broaden what is considered an allowable expense.
  • 1977– In response to the 1964 Alaska and 1971 Sylmar (California) earthquakes, the National Earthquake Hazards Reduction Act is enacted.
  • 1979– The Federal Emergency Management Agency (FEMA) was “charged with coordinating federal disaster policy including preparation, mitigation, response, and recovery”.
  • 1988– “The Robert T. Stafford Disaster Relief and Emergency Assistance Act established the statutory authority for presidential disaster and emergency declarations as well as the resulting federal assistance”.
  • 1993– Community Development Block Grant Disaster Recovery program funds were appropriated after Hurricane Andrew. They become a major part of federal recovery assistance.
  • 2000– In Response to Hurricane Fran, the states are encouraged to require enhanced mitigation planning.
  • 2006– “The Post-Katrina Emergency Management Reform Act reorganized FEMA by redefining its mission, consolidating its emergency management functions, and granting it greater autonomy”.
  • 2011– FEMA develops the National Disaster Recovery Framework to coordinate pre-disaster planning and facilitate post-disaster response across all levels of government.
  • 2012– The Biggert-Waters Flood Insurance Reform act tackles deficits in the flood insurance program that were generated by Hurricane Katrina.
  • 2012– The Hurricane Sandy Rebuilding Taskforce developed model resilience policies for vulnerable communities.
  • 2013– The Disaster Relief Appropriations Act of 2013 is created to fund several federal agencies for recovery operations due to Hurricane Sandy.
  • 2014– “The National Disaster Resilience Competition, an ongoing competition modeled on Rebuild by Design, made $1 billion available to communities to develop innovative resilience projects and plan for the effects of extreme weather and climate change”.

Natural Disaster Impacts

The top five deadliest hurricanes, tornadoes, and wildfires for the US, from 1970 to present, have been identified and details have been provided. Of all the natural disasters, Hurricane Maria has been the most devastating. Hurricanes, in general, killed more people, followed by tornadoes. Wildfires have killed the least number of people. The spreadsheet may be viewed here.

Research Notes

  • When researching hurricanes, the number injured was not shared with any of the top five deadliest hurricanes. This is most likely due to the devastating nature of the hurricanes and the mass confusion that comes with flooding.
  • The disasters that had the most research surrounding health and environmental effects were the older ones.
  • Wildfires are not necessarily measured by how deadly they are, but by how much acreage they destroy, as this is a better indicator of the effects on the area, environment, and economy.
  • Interestingly, none of the disasters that are on the list are the worst US disasters in history. These disasters all occurred in the late 1800s or early 1900s.
  • The project would benefit from further research that takes into account the economic damage as an indicator of the worst natural disasters, as this seems to be the one constant factor across the different types of disasters. For instance, wildfires historically do not kill large amounts of people, but the economic effects are significant and more inline with other disasters.
Glenn is the Lead Operations Research Analyst at The Digital Momentum with experience in research, statistical data analysis and interview techniques. A holder of degree in Economics. A true specialist in quantitative and qualitative research.


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