Dr. Pamela Grothe, Assistant Professor, University of Mary Washington
THE SCIENCE BEHIND CLIMATE CHANGE
Our understanding of the climate system is well established. According to the International Panel on Climate Change (IPCC)1, it is unequivocal that the increase of carbon dioxide (CO2) and other greenhouse gases in the atmosphere over the industrial era is the result of human activities. Greenhouse gases, most notably CO2, but also methane (CH4) and nitrous oxide (N2O), absorb energy emitted by the Earth and re-emit that energy back to the atmosphere. Adding greenhouse gases through burning fossil fuels is equivalent to adding an additional blanket over the Earth, trapping the heat and warming the planet.
Reconstructions of climate over thousands to millions of years show that atmospheric CO2 concentrations and global surface temperature are strongly coupled. Present-day CO2 levels have not been seen since four million years ago, a time just prior to Earth entering the current “icehouse” period that has controlled our climate over the last one million years.
However, the problem is not about the total concentration of CO2 and warming, but the rate of change. The IPCC states that the current warming trend is unprecedented in at least the last 2,000 years.
The best analogue to learn about the future impacts related to present-day climate change is an event that occurred over 50 million years ago – the Paleocene Eocene Thermal Maximum (PETM). During this time, a large source of CO2, equivalent to the total known fossil fuel reserves, was emitted into the atmosphere over 10,000 years, a rate still 1/10th of the present-day rate. During this event, extinctions occurred in the ocean due to ocean acidification and deoxygenation, and wholesale shifts in land mammals occurred. More importantly, it took 200,000 years for the Earth to recover – well beyond the lifespan of humans.
The increase in global surface temperature since the preindustrial is just over 1° C. Estimates of global temperatures exceeding 1.5° C, the target set by the IPCC to avoid the worst climate-related impacts, is expected to occur in the early 2030’s. This magnitude of change in warming is unprecedented in our lifetime and will require never seen before global collaboration in achieving net-zero emissions before reaching catastrophic levels of CO2 that could possibly drive humanity to the brink of destruction.
REGIONAL CLIMATE IMPACTS
The City of Fredericksburg is not immune to climate change impacts, including warmer temperatures, more extreme weather events, and sea level rise.
Heatwaves cause the largest weather-related illnesses and deaths and disproportionately impact marginalized communities. Cities are the most impacted by extreme temperatures, due to the Urban Heat Island Effect – they can be up to 10°C warmer than surrounding rural areas just due to the increase in heat-absorbing asphalt and lack of trees which provide cooling shade. Currently, Fredericksburg sees 12 more days per year in excess of 95°F, compared to 1950, and that number is expected to rise 2 to 3 times that in the coming decades3.
The atmosphere holds more water moisture when temperatures are warmer. As such, future projections of extreme precipitation events are expected to increase in many regions. In Fredericksburg, the number of heavy downpours has increased and is expected to increase more so. This extreme precipitation, coupled with urbanization (roads, parking lots, buildings, etc.), will lead to larger amounts of runoff and flooding and overwhelm drainage systems, damaging properties and polluting our water.
Globally, sea level has risen by 8-9 inches since the preindustrial, and even if we meet our climate emission goals, it will continue to slowly rise because of a lag in the ice response to a warming climate. Importantly, the regional rates of sea level rise are twice the global rates due to land subsidence from post glacial rebound and groundwater withdraw. Higher sea level is redefining the new high tide mark, submerging neighboring communities and streets during extreme high tides. Fredericksburg, which is partially located in the tidal zone, has already seen 1 foot rise in seal level since 1950 and is expected to see a rise of 2-6 feet by 20703.
Hurricane intensity is expected to increase due to rising ocean temperatures. Additionally, hurricanes will be wetter, with 10-15% more precipitation if warming reaches +2° C. This, coupled with sea level rise, will make them more damaging as storm surge will inundate farther inland. Furthermore, evidence suggests that hurricanes will track farther north in a warmer world potentially impacting the mid-Atlantic region more frequently.
ADAPTION
Though future climate change and impacts will depend on society’s ability to reduce greenhouse gas emissions, many of these impacts we are already committed to today. Therefore, the city must also consider adaptation measurements to protect human lives, health, and property from the impacts of climate change. ADAPTVA – short for Adapt Virginia is a great resource on climate change adaptation tools specific to Virginia4.
Fighting climate change needs to address both the root cause of a warming climate as well as adaptations to the impacts we already faced with today and those that are to come.
1IPCC, 2021: Summary for Policy Makers
2Figure – Modified from Scripps Institution of Oceanography and accessed from https://timescavengers.blog/climate-change/co2-past-present-future/
3Community Climate Outlook: Fredericksburg, VA accessed from https://www.marisa.psu.edu/misc/outlooks/community_climate_outlook.rev_2020-11-11.fredericksburg.pdf
