1.5°C and what it means for Virginia

Written by Dr. James Kinter and Dr. Barry Klinger

If there is one number that appears most often in climate discourse, it is 1.5 degrees Celsius (1.5°C). We see it in scientific reports, painted onto activists’ signs, and in the news. But, what’s so special about 1.5°C (2.7°F) and what does it mean for Virginia? There’s nothing magical about the number, but every increment of temperature above it increases the impact of global heating on everyone, including Virginians. 

In 2015, the nations of the world signed the Paris Agreement, the overarching goal of which is to hold “the increase in the global average temperature to well below 2°C above pre-industrial levels” and pursue efforts “to limit the temperature increase to 1.5°C above pre-industrial levels.” More recently, climate scientists and world leaders have stressed the need to limit global warming to 1.5°C. That’s because more recent scientific research indicates that crossing the 1.5°C threshold risks unleashing more severe climate change impacts, including more frequent and severe droughts, heatwaves, and rainfall. 

But this month, the World Meteorological Organization’s (WMO) annual Climate Update estimated that there is a 66% chance that at least one of the years between 2023 and 2027 will exceed 1.5°C.  The number refers to the temperature averaged over the entire surface of the Earth for the whole year.  We can think of this as a Global Heating (GH) Index.  Every place has its own temperature, but because global heating is – well – global, temperatures in many places tend to all rise together. Just as any one stock is more likely to be up when a stock market index (like the Dow Jones Index) goes up, your town is likely to be warmer when the GH Index is warmer. 

Higher temperatures melt glaciers and expand the ocean, raising water levels along the Virginia coast and in Tidewater rivers such as the Potomac and James.  Warmer air can contain more moisture, feeding worsening downpours and flash floods that strike across the Commonwealth in spring and summer.  Hotter air can also suck the moisture out of the soil more quickly, leading to more severe drought in western and southern Virginia.  Winters that don’t get cold enough to reduce tick populations raise the incidence of Lyme disease, especially in the mountainous western part of the state. 

Average annual temperature in Richmond, Virginia has increased 2.6°F since 1970.

Source: Climate Central

For the past 3 years, the GH Index was suppressed by a persistent “La Niña” condition in the tropical Pacific – an intermittent short-term climate shift where the surface of the ocean is a few degrees Celsius colder than the long-term average. The tropical Pacific is so big that a few degrees of cold cause the average over the whole globe to be a few tenths of a degree colder as well. This year we appear to be heading into a substantial “El Niño” condition, meaning the tropical Pacific Ocean will be warmer than the long-term average which can raise the GH Index to 1.5°C or higher. That warming is only temporary, but this illustrates how climate change works.  The combination of the long-term upward trend with short-term, random climate jumps can bring unpleasant surprises.  Similarly, we can be hurricane-free for many years and then a Category 5 storm, fueled by rising ocean temperatures, clobbers our coastal cities. Or drought is not normally a problem in Virginia, until a prolonged dry spell comes along and is made worse because of a global heating-induced heat wave.  The GH Index can show little change for a few years and then leap up almost 1°F, as it did in the 2010s.

Humans facing global heating are like people lying on the beach next to a rising tide. They see the waves getting closer but are too comfortable to get up and move the blanket. Maybe after lunch! Anyway, they know the tide takes hours to creep up the beach. But it’s not the tide that hits them; sooner or later there will be a wave that is bigger than the rest, and the combination of the rising tide and the big wave drenches their blankets and ruins their lunches.

We can’t do anything about El Niño, but we can do something to prepare ourselves for the new weather and climate extremes. The WMO report highlights the urgency of the situation: communities in the Commonwealth, especially our most vulnerable communities, must increase their resilience to the impacts of extreme heat, extreme precipitation, extreme weather, and sea level rise. Furthermore, Virginia’s communities must continue to take bold steps to mitigate future warming by cutting their emissions of heat-trapping greenhouse gases – by reducing their dependence on fossil fuels and transitioning to clean renewable energy sources.  The faster Virginia and the world transition to clean energy, the less we will push the GH Index into the danger zone above 1.5°C. 

Authors

Dr. James Kinter

Dr. Kinter is lead PI for the Virginia Climate Center and a Professor in the Department of Atmospheric, Oceanic, and Earth Sciences at George Mason University

Dr. Barry Klinger

Dr. Klinger is a Faculty Affiliate for the Virginia Climate Center and a Professor in the Department of Atmospheric, Oceanic, and Earth Sciences at George Mason University