Climate Change Impacts & Projections for the Greater Boston Area
Written By Yve Torrie, Director of Climate, Energy & Resilience
On July 22nd, A Better City co-hosted an event with the Boston Green Ribbon Commission, Climate Change Impacts and Projections for the Greater Boston Area, to understand the latest climate projections for the Greater Boston region. In 2016, a group of scientists known as the Boston Research Advisory Group (BRAG), led by UMASS Boston, presented the first scientific consensus on climate change impacts specifically related to the City of Boston. These projections formed the basis of the City’s Climate Ready Boston report. The BRAG was tasked with updating these projections every five years. The latest climate projections updated and expanded the analysis to investigate climate changes and threats to the entire Metropolitan Area Planning Council (MAPC) region, including the 101 cities and towns within the Greater Boston Area.
Six prominent scientists at the event discussed the climate projection findings for Greater Boston, released in the report, Climate Change Impacts and Projections for the Greater Boston Area. These scientists were: Paul Kirshen, project co-lead, who is Professor of Climate Adaptation at UMASS Boston’s School for the Environment; Ellen Douglas, project co-lead, who is Associate Dean and Professor of Hydrology at UMASS Boston’s School for the Environment; Rob DeConto, Professor and Co-Director of UMASS Amherst’s School of Earth & Sustainability; Ambarish Karmalkar, Affiliated Investigator and Research Assistant Professor at UMASS Amherst’s College of Natural Sciences; Mathew Barlow, Professor at UMASS Lowell’s College of Science; and Jayne Knott, Principal and Senior Scientist at JFK Environmental Services, LLC.
The key climate projections were summarized as follows:
- Average annual temperatures could be approximately 3 to 10℉ greater by 2100 compared to the start of the century, depending upon location and whether greenhouse gas emissions are moderate or high. The number of days over 90 ℉ could increase from approximately 10 days/year to 20 to 80 days/year, depending on future emissions. Temperature increases are expected to cause losses in some of Massachusetts’ signature industries, including cranberries, maple syrup, Cape-caught lobsters, and shellfish, and a reduction in winter sports due to lack of snow.
- Consequences for human and economic health include as much as a 12 percent increase in residential electrical energy costs and rising heat-related mortalities by 2050 – these impacts will disproportionately affect marginalized and socioeconomically vulnerable populations.
- Heat-related impacts will be felt most acutely in urban heat islands, which are often populated by people that have been marginalized and oppressed. These communities will be at greater risk of experiencing impacts of excessive heat and poor air quality, including mortalities, as well as economic stressors associated with increased energy costs, and disruptions to public transportation.
- Groundwater levels have increased over the last 50 years. Over the next 50 years, groundwater recharge is projected to increase in the late fall and early winter with increased precipitation but to decrease sharply during late winter and spring due to reduced snowpack and increased evapotranspiration.
- Annual average recharge is projected to decrease by approximately 18 percent towards the end of the century (depending on the location) even with the lower emissions scenario – potentially resulting in less available drinking water.
- The quality of drinking water in coastal areas will also be reduced as salt water intrudes into groundwater aquifers. Groundwater levels in coastal areas may increase due to this saltwater intrusion.
- Compared to surface water, groundwater contributes to a much greater percentage (52–76 percent) of potable water withdrawals in Norfolk, Plymouth, and Middlesex counties. Over the next century, it will be important for counties to balance drinking water demand with projected decreases in groundwater availability.
Sea-Level Rise and Coastal Flooding:
- Median sea-level rise for Boston Harbor is expected to be 3.4 feet by 2100 under a high emissions scenario, though greater than 10 ft of sea-level rise is still possible. Uncertainty in the behavior of Antarctic ice sheets and in future greenhouse gas emissions still drive uncertainty in sea-level rise projections.
- If greenhouse gas emissions continue to increase, Boston will see more nuisance flooding days, which are days in which the local flood threshold is exceeded for at least an hour. By 2050, nuisance flooding may occur in Boston Harbor on roughly half the days each year. Presently it is less than approximately 15 days each year.
- Even with lowered greenhouse gas emissions, what is now a 1 in 10-year flood could be an annual occurrence by 2050. Under higher emissions scenarios, our current 1 in 100-year flood events would likely become an annual flood by 2100 or sooner.
River and Stormwater Flooding:
- The 2022 update increases confidence in 2016 projections of a 20–50 percent increase in small (e.g., two year) river floods and a 15–70 percent increase in 100-year river floods by 2100, and states that these projected increases in flooding can no longer be considered conservative estimates.
- As snowfall shifts to rainfall in late winter and early spring, when there is less plant growth to absorb the extra water and precipitation events become more intense, we will see increased stormwater runoff and pluvial flooding. This excess water can impact wildlife species and stress human developments and infrastructure, resulting in increased costs to repair damaged systems and property.
- The increase in the amount and intensity of precipitation will increase flood risk in all of the communities studied, though with different manifestations for coastal vs. inland areas. In coastal areas, increased precipitation may combine with higher groundwater tables and sea levels to exacerbate damage from storm surge. For inland areas, river and flash flooding due to more intense rainfall, soil saturation, and changing plant diversity will predominantly drive flood risk.
Storms and Precipitation:
- There is more certainty on the effect of climate change on storms. The strength of extratropical storms may decrease but the proportion of stronger tropical storms is expected to increase. For all types of storms, precipitation intensity is expected to increase.
- Annual precipitation has increased in the Northeast. Increased winter and spring precipitation could cause a continued increase in annual precipitation, but this remains highly uncertain. As the City of Boston currently experiences relatively consistent rainfall year-round, changes in seasonal precipitation variability introduces another factor to consider in flood mitigation planning.
- Most projections point to a 10–20 percent increase in daily precipitation intensity by 2050 and a 20–30 percent increase by 2100, impacting existing and future developments, public infrastructure, stormwater and watershed management, and agriculture.
- The projected increases in daily and annual precipitation, coupled with decreased groundwater recharge, will have wide-reaching consequences on infrastructure, food production, and the availability of drinking water.
The discussion that followed touched on some important themes:
- Uncertainty: How do we convey the urgency of this to the public and policymakers? Panelists said we all deal with uncertainty in our lives, we always make choices under uncertainty, but we just continue to hope that things are constant! We need to take the blinders off and understand there is a lot of uncertainty in our future that we need to plan for.
- Optimism related to climate projections:
- We are no longer on the worst-case emissions scenario trajectory; we have moved away slightly in the right direction, unrelated to COVID’s impact.
- While there’s a large response needed to climate change, it can also solve a lot of problems and can be an opportunity. We must change infrastructure and energy uses but there are a lot of other positive outcomes we can wrap into that like more efficient housing, more green spaces, and the increased health of our population. Nature based solutions to resiliency, for example, end up having enormous co benefits to local ecosystems, local economies, and local environment justice communities while also contributing to mitigation through carbon absorption.
- Adaptation planning investment is worth it with every dollar spent saving $5-10 in future costs.
- The cost of renewable energy has plummeted, and market forces are showing that emissions reductions can make financial sense.
- Stark reality of climate projections:
- The United Nations Framework Convention on Climate Change (UNFCCC)’s Paris Agreement, updated in Glasgow last year, has a goal to limit global warming to 2 degrees Celsius compared to preindustrial climate but with the ambition to try to keep global temperatures from rising by 1.5 degrees Celsius. We are already at 1.2 degrees warmer.
- While it’s not too late to achieve net-zero emissions by 2050, there is now only limited time to implement changes that will contribute to preventing the worst-case scenarios projected in this report.
There is a lot we can do at a municipal and state level, and there was a discussion about the development of a regional climate authority, like MWRA. As some adaptation actions require coordination across political boundaries there was a consensus that a regional governing would be beneficial.
For any questions or comments, please contact Yve Torrie.