Jeff Masters Weather Blog

The massive smoke plume choking the northeast U.S. is what climate change looks like » Yale Climate Connections

Some of the most intense, dramatic wildfire smoke in memory swept into the northeast United States on Tuesday, June 6, pushing pollution levels in some cities to record highs. Millions of people from the U.S. mid-Atlantic to southeast Canada were confronted on Tuesday and again on Wednesday by surreal, copper-yellow skies and shrouded horizons.

Portions of five states and two Canadian provinces experienced 24-hour levels of fine particle pollution, known as PM 2.5, in the “Unhealthy” (red) range, with even higher levels measured on an hourly basis. According to the U.S. Environmental Protection Agency, at that level, everyone may begin to experience health effects, and members of sensitive groups may experience more serious health effects. Near Canada’s capital city of Ottawa, 24-hour PM 2.5 levels were in the “Very Unhealthy” (purple) range. According to the EPA, this level of pollution triggers a health alert, meaning everyone may experience more serious health effects.

a map shows unhealthy air spreading over large sections of New York, Pennsylvania, and Connecticut
Figure 1. The daily EPA Air Quality Index (AQI) for June 6, 2023. Portions of five states and two Canadian provinces experienced “Unhealthy” air (red colors). (Image credit: U.S. Environmental Protection Agency.)

The smoke was belching from dozens of wildfires burning across Quebec, which has experienced its hottest, driest late spring on record, as has much of Canada. As noted by Capital Weather Gang, New York City, Detroit, and Toronto ranked at one point on Tuesday as three of the 12 most polluted major cities on Earth.

Read: How to protect yourself from wildfire smoke

At a news conference Wednesday morning, New York City Mayor Eric Adams said, “This is an unprecedented event in our city and New Yorkers must take precautions. We recommend vulnerable New Yorkers stay inside … This is not the day to train for a marathon.” He added: “Climate change has accelerated these conditions. We must continue to draw down emissions, improve air quality, and build resiliency.” New York City recorded its highest daily levels of PM 2.5 pollution on record Tuesday, reaching an AQI of 174 in Queens.

Conditions are predicted to be even worse in many areas on Wednesday and Thursday, as another major plume of thick smoke works its way southward from Quebec through the Northeast U.S. More grim news: the broader weather pattern – with the main jet stream pushed all the way to the Arctic by relentless, summerlike high pressure across the heart of North America – may continue stoking widespread fire in Canada and periodic infusions of smoke into the U.S. for days to come.

a map shows a forecast for moderately unhealthy air over much of the eastern U.S., including unhealthy air over the Northeast. On the right, a second map shows a forecast for slightly improved conditions June 8.
Figure 2. AQI forecast for PM 2.5 for Wednesday (left) and Thursday (right) from the EPA.

At 10 a.m. EDT Wednesday, June 7, the worst air in the U.S. was in Syracuse, New York, which had an hourly PM 2.5 AQI of 402 — well into the “Hazardous” range. EPA warns that an AQI in this range will “trigger health warnings of emergency conditions. The entire population is even more likely to be affected by serious health effects.” Syracuse set an all-time record on Tuesday for the highest 24-hour PM 2.5 levels, and that record will likely be broken again today.

What caused the wildfires in Canada?

Canada’s spring of fire began in Alberta. The same wintertime pattern that focused torrential rains and mountain snows across California and the U.S. Southwest left much of western Canada high and dry.

An unusually large and strong area of high pressure then intensified at upper levels over central North America during May, keeping precipitation at bay and allowing temperatures to hit summertime levels across much of southern Canada and the far northern U.S. Readings soared well above 90°F in many unorthodox places, including Seattle (91°F on May 15).

The heat, in turn, parched the landscape and set the stage for springtime fires, initially in Alberta during mid-May. Smoke aloft filtered into the Midwest and Northeast, while the Denver area experienced close to a week of severely polluted surface air in late May.

By late May and early June, the dangerous fire weather extended into the moister climates of Ontario and Quebec — and even the Canadian Maritimes — as lush trees and grasses became tinder-dry amid severe drought and heat.

As of June 6, more than 150 wildfires were burning in Quebec, including more than 110 raging out of control, while Ontario was dealing with 47 active wildfires. According to Quebec’s fire prevention agency, SOPFEU, the province typically sees 794 hectares burned by June 6 (10-year average). This year, the total to date is an astonishing 473,656 hectares.

“We’re experiencing an unprecedented situation, exceptional, everywhere on Quebec territory,” François Bonnardel, the province’s public security minister, told CTV News. “We’ve never had so many fires so early in the season. It’s not just a problem for Quebec, it’s a problem all over Canada.”

Michael Norton, an official with Canada’s Natural Resources ministry, told Reuters: “The distribution of fires from coast to coast this year is unusual. At this time of the year, fires usually occur only on one side of the country at a time, most often that being in the west.”

A stuck weather pattern across the continent

The same upper high that’s spawned fire in Canada has kept the jet stream well north of the U.S. for much of this spring, leaving large parts of the nation weirdly stagnant. Days of slow-moving showers and thunderstorms have drenched a belt from Texas to Colorado, helping quench a three-year drought on the High Plains. Meanwhile, many locations farther east have seen mostly stagnant air and little rainfall.

The connection between climate change and wildfires

Fire is a natural feature of North American ecology. However, dangerous fire weather has surged more quickly than expected as a serious consequence of our human-warmed climate. In regions where fire is a perennial part of the climate, such as the western U.S. and Canada, rising temperatures have prolonged the fire season, allowing fires to burn more widely and for longer periods. It’s this seasonal fingerprint that jumps out as the prime climate-change signal in the southern Canada fires and the bizarre, ongoing smoke episode of early June in the northeast U.S.

Even the colossal fires that torched parts of the U.S. West and Midwest — including Chicago— during the timber-harvest runs of the late 19th and early 20th century tended to occur in summer or autumn, not in late spring.

Fires and floods be difficult to project in climate-change simulations, because they depend not only on atmospheric changes but also on aspects of the built landscape (e.g., an expansion of paved areas that allow water to flow more readily, or an increase in homes in the wildland-urban interface). But we can look more directly at changes in fire weather days — those days that pass various risk thresholds of low humidity, high heat, and strong wind.

In an analysis released May 23 that draws on data from 476 U.S. weather stations, Climate Central showed that fire weather days are occurring over longer, more intense fire seasons, especially in the western United States.

“Southern California, Texas, and New Mexico have experienced some of the greatest increases in fire weather days each year, with some areas now seeing around two more months of fire weather compared to a half-century ago,” the report noted. It added: “Even small increases in fire weather in the East, which has nearly 28 million homes located in zones prone to burn, puts more people at risk.”

a map shows that fire weather days are becoming more common in the U.S. Southwest
Figure 2. Change in the number of fire-weather days per year, by U.S. climate region, from 1973 to 2022. (Image credit: Climate Central)

Another recent study took a global look at potential changes in fire weather this century, using the Canadian Fire Weather Index and drawing on output from the suite of climate models used in the most recent IPCC assessment, a sweeping report periodically issued by the world’s top climate scientists. The projections suggest that the average fire duration could triple, and average fire intensity could jump by 31% — but with much regional variation — for a higher-end amount of global warming (3°C above preindustrial values).

According to the study, “for most regions of Earth and incremental warming levels, all four annual indicators show an increase in their average, even if this signal is not robust in all regions.”

Comparison with the wildfire event of July 7, 2002

Records for the worst PM 2.5 levels in modern record-keeping were set at numerous locations in the Northeast on Tuesday, beating the previous all-time records (with data back to 1999) set on July 7, 2002, when a similar wildfire-smoke episode hit the region. According to NASA Earth Observatory, on that day there were 40 wildfires in Quebec, at least seven of which were burning out of control, causing several hundred people to be evacuated. Most of the fires were caused by lightning.

Some all-time records for PM 2.5 AQI from the 2002 event, which were beaten on Tuesday, include:

Bridgeport, Connecticut (4 sites): 165 (new record: 166)
Syracuse, New York (2 monitors): 142 (new record: 169)
New York City region (31 monitors in NY, NJ, PA): 167 (new record: 174)
Scranton, Pennsylvania (2 monitors): 154 (new record: 175)

a chart shows that the air quality in the New York City metro area is the worst it's been in about 20 years, with one exception in July 2021
Figure 3. Air pollution history for daily maximum PM 2.5 from 1999 – 2023 in the New York City metropolitan area (31 monitors in NY/NJ/PA). Before June 6, 2023, the city’s highest PM 2.5 reading was an AQI of 166, from a smoke episode on July 7, 2002, caused by Quebec wildfires. Yesterday’s AQI at a monitor in Queens hit 174, establishing a new record for the New York City area. (Image credit: EPA)

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