Expansion of the Lyme Disease Vector in Canada Inferred from CMIP5 Climate Projections

Background: A number of studies have assessed possible climate change impacts on the Lyme disease vector, . However, most have used surface air temperature from only one climate model simulation and/or one emission scenario, representing only one possible climate future.

Objectives: We quantified effects of different Representative Concentration Pathway (RCP) and climate model outputs on the projected future changes in the basic reproduction number (R) of to explore uncertainties in future R estimates.

Methods: We used surface air temperature generated by a complete set of General Circulation Models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to hindcast historical (1971-2000), and to forecast future effects of climate change on the R of for the periods 2011-2040 and 2041-2070.

Results: Increases in the multimodel mean values estimated for both future periods, relative to 1971-2000, were statistically significant under all RCP scenarios for all of Nova Scotia, areas of New Brunswick and Quebec, Ontario south of 47°N, and Manitoba south of 52°N. When comparing RCP scenarios, only the estimated R mean values between RCP6.0 and RCP8.5 showed statistically significant differences for any future time period.

Conclusion: Our results highlight the potential for climate change to have an effect on future Lyme disease risk in Canada even if the Paris Agreement's goal to keep global warming below 2°C is achieved, although mitigation reducing emissions from RCP8.5 levels to those of RCP6.0 or less would be expected to slow tick invasion after the 2030s. https://doi.org/10.1289/EHP57.