Dr. David R. Legates is a retired University of Delaware professor, a former state climatologist and the director of research and education at the Cornwall Alliance for the Stewardship of Creation.
On March 24, the Delaware Department of Natural Resources and Environmental Control posted a statement to its Facebook account that highlighted the recent Frederica tornado and severe winds in Kent County. It concluded: “This is what climate change looks like in Delaware.”
Was the tornado in Frederica caused by climate change? While it is impossible to determine that climate change caused any single event, we can assess whether tornadoes and the other “emergent hazards” in DNREC’s post are becoming more frequent in Delaware. Let’s look at what Delaware’s data shows.
Tornadoes and extreme storms
A review of the National Oceanic and Atmospheric Administration’s Storm Events Database provides data on tornadoes recorded in Delaware from 1950 to the present.
NOAA’s records show that Delaware’s annual tornado counts have varied since 1950, with some quiet years and some active ones, but no clear increasing trend over time. Looking at the number of days with a recorded tornado tells a similar story: a lot of variability but no obvious upward pattern.
This does not mean tornadoes are unimportant, only that our long-term records here do not show the steady rise implied by DNREC’s phrase, “more frequent tornadoes and extreme storms.”
Vector-borne diseases
DNREC also warns of “expanding vector-borne diseases like Lyme and West Nile virus.” The State Surveillance System, Delaware Division of Public Health publications and the Delaware Office of Infectious Disease Epidemiology give data on Lyme disease and other mosquito- and tick-borne disease occurrences in Delaware.
This surveillance data confirms that Delaware remains a high-incidence state for Lyme disease and that tick- and mosquito-borne illnesses are a serious concern. However, when you line up the annual case counts over the last couple of decades, they rise and fall from year to year, rather than following a simple, steadily increasing line.
The pattern is messy, not a smooth climb that can clearly be attributed to rising greenhouse gas concentrations alone. While this is certainly not an argument to be complacent about disease risk, it does show that Delaware’s numbers do not match DNREC’s suggestion of a straightforward, climate-driven increase.
Coastal waters, wildfires and droughts
DNREC next points to “ocean and coastal acidification” and “increased wildfire and drought risk.”
Acidification is measured by the pH level — the concentration of hydrogen ions in a liquid solution — with lower values being more acidic and higher values being more alkaline or basic. The longest records of data are available for Scotton Landing (at the Delaware National Estuarine Research Reserve, near Kitts Hummock) and Blackbird Landing (near Townsend) from the NOAA National Estuarine Research Reserve Systemwide Monitoring Program.
Now, let’s consider data on wildfires in Delaware. The data is taken from the Fire Program Analysis fire occurrence database and covers the period from 1992 through 2020.
Wildfire records for Delaware show relatively few fires most years, with one standout season in 2002, when 12 fires burned about 1,500 acres. Outside of that outlier, there is no clear upward trend in either the number of fires or the total acreage burned.
And, finally, drought risk: NOAA keeps track of droughts using the Palmer Drought Severity Index and the Palmer Hydrological Drought Index. The PDSI is used for general monitoring of hydrological conditions, while the PHDI is useful for long-term water deficits.
These indexes, which go back to 1895, show that Delaware cycled through wet and dry periods over time, including major droughts in the 1930s, the mid-1960s and the recent event we are now emerging from. Despite that variability, there is no obvious long-term increase in drought conditions in these indexes that can be tied specifically to rising greenhouse gas concentrations.
House Bill 99 and Delaware’s Climate Action Plan
So, why did DNREC make this post on Facebook? The final sentence tells it all: “But Delaware has a plan.”
The 2025 Climate Action Plan is described as “our statewide playbook for building resilience and reducing the emissions driving these threats.”
When the Delaware General Assembly passed House Bill 99 (the Delaware Climate Change Solutions Act of 2023), and it was signed into law, the state established targets of at least 50% reduction below 2005 emission levels by 2030 and net zero emissions by 2050. To accomplish this, Delaware’s Climate Action Plan lays out a wide range of measures across the transportation, industry, energy, agriculture, the economy and education sectors, and directs state agencies to incorporate climate strategies into their decision-making and to appoint climate change officers across key departments.
Delaware’s emissions, however, are a very small fraction of global greenhouse gas totals, so even full compliance with these targets would have no measurable effect on global climate by itself. The measures needed to reach those goals, however, are likely to impose substantial costs on Delaware’s economy and could significantly affect daily life in the state.
Conclusion
As John Adams famously quipped in 1770, “Facts are stubborn things.” Delaware’s own records on tornadoes, vector-borne diseases, coastal conditions, wildfires and droughts do not show the clear, worsening trends implied by DNREC’s recent post.
DNREC is right to care about public safety and long-term risk, but a better approach is to ground our climate and energy policies in what the data for our state shows — and to weigh carefully the real benefits and costs of mandates like those in HB 99 and Delaware’s Climate Action Plan.
Reader reactions, pro or con, are welcomed at civiltalk@iniusa.org.
