Introduction: Land and Living Systems
Land and Living Systems
As climate change raises temperatures and changes the weather worldwide, it’s also changing the rules of the game for living things on land. Spring is starting earlier, hotter weather is leading to more wildfires, frozen Arctic soil is melting, and seasonal events like migrations and tree leafing are happening at different times.
Credit: John A. Kelley, USDA Natural Resources Conservation Service
Soil that stays frozen throughout the year is called permafrost. In Alaska and other place around the Arctic, permafrost is shrinking over time as temperatures warm.
Change Begets More Change
Climate change is altering many of Earth’s ecosystems. It might make the food animals eat more scarce, cause natural events like migrations to happen at the wrong times, or make the climate too hot or too dry for young animals to survive.
Even as climate change hurts some species, it could help others, at least in the short term. But with so many different factors changing at once, the overall impact will be massive. And species that can’t adapt to this altered world could disappear forever.
Dataset Wildfires on the Rise
Wildfires on the Rise
As the climate changes, higher temperatures are creating drier vegetation—conditions that favor more frequent and more intense wildfires. This map shows the number of wildfires across the globe over the last 10 years.
Fires on Earth’s surface, as detected by infrared, or heat radiation, sensors on NASA’s MODIS satellite. Source: NASA Earth Observatory, NASA Goddard Space Flight Center
How Does Climate Change Lead to More Wildfires?
As climate change causes global temperatures to rise, summers are becoming hotter and longer, which helps to dry out trees, grasses, and other plants. Drier plants burn much more easily.
The longer warm season also means that snow is melting earlier. In places like California, where it rarely rains in the summer, this means there’s much less water in the soil for plants to absorb.
In 2015, researchers discovered that fire season in the Western United States now lasts seven months instead of five months. Globally, the fire season was 19% longer in 2013 than in 1979.
California’s snowpack, its moisture reserves for the year, has been below average more often in recent years. Source: Based on graph from California Department of Water Resources
Providing the Spark
In addition to creating dry conditions, climate change may sometimes help to ignite wildfires. In hotter weather, lightning strikes more often—one study suggests that for every one degree Celsius temperature increase, the United States will get 12% more lightning strikes. (However, the great majority of wildfires are started by human activities.)
Credit: U.S. Forest Service
In 2015, Alaska's Aggie Creek Fire burned for more than two months, scorching some 30,000 acres.
More Fires Already?
Climate change may already be increasing the number of wildfires. For example, one study found that nearly twice as much land area burned in 2015 as in 1984. However, while climate change has contributed to this increase, there are many other factors involved, such as how we fight fires, and how we manage our forests and vegetation to prevent fires.
Wildfires Also Make Climate Change Worse
As a wildfire consumes trees, it transforms the tree's carbon—which is most of its mass—into carbon dioxide. In northern forests, fires also burn peat, the carbon-rich soil beneath the forest, releasing more carbon dioxide. This extra carbon dioxide traps more heat in the atmosphere, further warming Earth.
On the other hand, the tiny particles in fire smoke—called aerosols—block sunlight in the atmosphere, which has a temporary cooling effect on the climate. But even taking that into account, wildfires have a net warming effect on the climate.
Credit: National Park Service
The 2013 Alum Fire at Yellowstone National Park, Wyoming, was started by lightning and burned more than 7,000 acres.
Dataset The Index of Spring
The Index of Spring
Is climate change causing spring to arrive earlier? The map below shows the timing of spring, based on when leaves first appear on lilacs and honeysuckles—among the first plants to sprout leaves each year. Red colors on the map mean that spring arrived earlier than usual, while blue colors mean that spring arrived later than usual.
The First Leaf Index, presented by the National Phenology Network, shows differences from the average leafing dates for cloned lilacs, common lilacs, and two species of honeysuckle, as reported by thousands of observers across the country. The averages are for 1981–2010. Source: National Phenology Network
Several studies of the First Leaf Index and similar records have found that in recent decades, spring is starting earlier. One 2016 study of 276 U.S. National Parks showed that in 76% of the parks, spring started earlier than average, and in 53% of parks, recent springs were among the earliest ever observed.
The first sprouting of leaves and blooming of flowers are strongly affected by the weather, and thus by climate change. Many plant species need a certain number of warm days (above a minimum temperature) to start growing leaves. When those warm days happen earlier, the leaves sprout sooner. Other factors may be involved, such as the amount of precipitation, and the number of cold winter days.
In California’s Central Valley, the first flight of the Red Admiral butterfly is happening 28 days earlier than it did in the 1970s. It’s one of many butterfly species whose life cycles have shifted with the warming climate.
Why It Matters
An earlier spring might cause problems for plants. They might be more vulnerable to attacks from pests, invasive species, fires, or they might simply shift their geographical range toward cooler temperatures, which could disrupt the other organisms that depend on that plant.
You Can Help
The National Phenology Network invites the public to help them measure the timing of spring. Even if your yard doesn’t have lilacs or honeysuckles, you can submit observations of other plant and animal events happening in your yard or other nearby habitats. Visit their Nature’s Notebook website to find out how to get started.
More Sites about Observing Spring
Dataset Leafing Dates of Oak Trees
Leafing Dates of Oak Trees
In England each spring, as the weather gets warmer, oak trees burst forth with a riot of tiny, green leaves amid the fading chill of winter. In 1947, a woman named Jean Combes began to write down the date each year when the first oak leaves appeared in her southeast England town of Ashtead.
The leafing dates of oaks in southeast England shifted earlier over 67 years of observations, begun by Jean Combes. Source: Based on graph from Woodland Trust
When Combes started observing, the oaks near her home sprouted leaves in early May. But as this graph shows, the dates trended earlier and earlier as the years went by. In 2017, the oaks regularly sprouted leaves a full month earlier than they did in 1950.
Credit: Martina Prohaczkova
English oak buds are sprouting new leaves.
Earlier Leaves, Warmer Temps
Leafing dates vary quite a lot from one year to the next. Oaks tend to sprout earlier when the spring weather is warmer, but other factors can also affect the leafing date.
Temperature anomalies in the United Kingdom—how much the temperature differed from the average (between 1961–1990). The clear warming trend since 1950 fits well with the earlier oak leafing dates observed by Combes. Source: Based on Wikimedia Commons graph of data from Met Office Hadley Centre
Jean Combes wasn’t the first Brit to watch the oak leaves. Robert Marsham, 1708–1797, is considered the founder of the field of phenology—the study of the timing of natural events. Marsham studied a wide variety of seasonal events, including leafing dates for 13 trees, flowering dates for plants, the arrival or first song of migrating birds, and the breeding of frogs and toads. His descendants continued collecting this data after his death, until 1958.
Because of Marsham’s careful record-keeping, we can easily compare observations today to what happened before the Industrial Revolution, when the use of fossil fuels began to increase, forcing the climate to change.
A chart published by Robert Marsham in his Indications of Spring, a book that chronicled his observations over 60 years.
More Sites about Oak Leafing
Dataset Case Study: The Birds Who Arrived Too Late for Lunch
Case Study: The Birds Who Arrived Too Late for Lunch
The European pied flycatcher is suffering from the effects of climate change. Rising temperatures are causing its food source—oak tree caterpillars—to appear weeks earlier than before—too early for its offspring.
Credit: Francesco Veronese
European pied flycatcher is about five inches long. The word “pied” in its name means something having two colors.
A Carefully Timed Migration
The European pied flycatcher—a bird small enough to fit in your hand—flies thousands of miles each spring from West Africa to Europe to nest in oak trees.
It used to be that flycatcher eggs would hatch at just the right time—when the trees were crawling with caterpillars for the baby birds to eat. But in recent years, when the baby birds hatch the caterpillars are often nowhere to be found. Source: Based on map from Carnivora.net
Winter oak moth caterpillars feed on new oak leaves in the spring.
What’s Going On?
Because spring temperatures are warming, oak leaves are sprouting earlier, causing the caterpillars to hatch up to 20 days sooner than they used to—long before flycatcher chicks are ready to eat them. The flycatchers can’t simply migrate earlier, because they start their migrations in response to the days getting longer in West Africa; and day length is not affected by climate change.
Flycatcher Populations Drop
So how do the baby birds survive with no caterpillars to eat? Many of them don’t. The study found that flycatcher populations in the Netherlands declined by more than 90% between 1995 and 2015.
Because pied flycatchers are widespread in Europe, their species is not threatened. But their story suggests that their might be other more fragile migratory birds with mistimed migrations. And they might not fare so well.
Dataset Defrosting Permafrost
Permafrost is ground that stays frozen for two years or longer. There’s a thin layer of surface soil on top of the permafrost that thaws and refreezes each year—the active layer. If the active layer stays thawed longer, then the permafrost beneath may start to shrink.
The map above shows permafrost in Arctic areas, such as Alaska, Canada, and Russia. Red colors mean the active layer thawed for longer than average; blue colors mean it was frozen longer than average. (The average is for 1979 to 2012.) The graph gives an overall indication of Arctic thawing, year by year. See the full animated dataset from 1979 to the present. Source: National Snow and Ice Data Center
Are We Losing Permafrost?
Permafrost covers almost 25 percent of the land in the Northern Hemisphere, but it may be shrinking. Temperatures are warming faster in the Arctic than anywhere else. As soil in the active layer thaws out for longer periods (map above), the permafrost underneath melts. This can be hard to monitor, since permafrost is underground, but research suggests that between 1995 and 2005, the southern boundary of the permafrost zone retreated by about 50 kilometers (30 miles).
The white areas have continuous permafrost (underlying 90–100% of the land area). The gray areas have discontinuous permafrost (50–90% of the area), sporadic permafrost (10–50%), or isolated permafrost (less than 10%). Source: Global Terrestrial Network for Permafrost
Melting Permafrost = Unstable Ground
The ice in permafrost acts like cement, holding together a mass of frozen rock and soil. When that ice melts, the ground above weakens and may even collapse under the weight of a building or a road. So in Alaska and other northern locales, melting permafrost is expected to cause billions of dollars in damage to towns, bridges, roads, and other infrastructure.
When permafrost ice (white) melts, the weakened soils may collapse and sink, especially under the weight of buildings or roadways. Along shorelines, melting permafrost is extremely vulnerable to erosion from ocean waves.
Credit: Mad Mikes America
The town of Newtok, in western Alaska, is severely threatened by river erosion due to melting permafrost. In 2017, with several homes in danger of collapse in the next year, Alaska and Federal authorities granted $1.7 million to help relocate residents to a safer site upriver.
A Vicious Melting Cycle
Melting permafrost can also make climate change worse by releasing trapped carbon dioxide and methane, gases that trap heat in Earth’s atmosphere. Because permafrost originally formed thousands of years ago during the last ice age, it contains the frozen remains of animals and plants. As permafrost melts, microbes break down those remains, converting the carbon in them to carbon dioxide (CO2) and methane (CH4).
Credit: Brandt Meixell, US Geological Survey
Permafrost sometimes doesn’t look frozen from the surface, but erosion sometimes offers a glimpse of the frozen, icy soil underneath and the active layer above, which only freezes during the winter.
More Sites About Permafrost