The feeling that weather is becoming increasingly erratic, unpredictable, or stuck in a pattern of extremes is a widely shared experience. Examples include summers that feel unusually hot for prolonged periods or winters that swing dramatically from mild to frigid. The underlying reasons for these unusual patterns are not singular, but rather a complex interplay of natural Earth cycles and profound changes to the atmosphere driven by human activity. This shift is altering the boundaries of what was once considered normal for local weather.
Understanding Weather Versus Climate
Distinguishing between weather and climate is the first step in understanding unusual atmospheric conditions. Weather describes the short-term state of the atmosphere, encompassing conditions like temperature, wind, and precipitation over minutes, hours, or days. It is what you experience daily.
Climate, conversely, is the long-term average of weather patterns in a specific region, typically calculated over a 30-year period. Climate represents the expected range of conditions, while weather is the actual, momentary event. When people perceive the weather as “weird,” they are noticing that short-term events are increasingly falling outside the expected range established by long-term climate norms. Changes to the global climate shift those underlying boundaries, making previously rare or extreme weather events more probable.
Natural Cycles That Drive Variability
The Earth’s weather is constantly influenced by powerful, recurring natural cycles that drive significant short-term changes. One of the most prominent is the El Niño Southern Oscillation (ENSO), which involves fluctuating sea surface temperatures in the central and eastern tropical Pacific Ocean. ENSO alternates irregularly between its two main phases, El Niño and La Niña, typically repeating every two to seven years.
During the warming El Niño phase, warmer Pacific waters influence global atmospheric circulation, leading to characteristic shifts in temperature and rainfall. For example, El Niño often brings warmer-than-average winters to the northern United States and Canada, while contributing to drought in Australia and Southeast Asia. The opposite La Niña phase, characterized by cooler Pacific waters, produces different global impacts, such as increased tropical cyclone activity in the Atlantic.
Another significant driver is the Arctic Oscillation (AO), a large-scale fluctuation in atmospheric pressure between the Arctic and the mid-latitudes. The AO alternates between positive and negative phases, dictating the strength and path of the polar Jet Stream. A positive AO phase keeps cold air locked over the Arctic, resulting in milder mid-latitude winters. The negative AO phase weakens circulation, allowing frigid polar air masses to spill southward into North America and Eurasia. These natural oscillations are responsible for much of the year-to-year variability in global weather.
How Climate Change Amplifies Extremes
The primary reason for the increased intensity of “weird” weather is the addition of excess energy and moisture into the Earth’s atmosphere, driven by human-caused climate change. As the planet’s baseline temperature rises, the atmosphere can hold significantly more water vapor. The atmosphere’s capacity to retain moisture increases by approximately 7% for every 1°C rise in temperature.
This increase in atmospheric moisture directly fuels the intensity of heavy rainfall events and flooding. When weather systems draw on this warmer, moister air, they unleash significantly more precipitation than would have been possible in a cooler climate. This means that what was once a 100-year rainfall event is now occurring with much greater frequency.
The overall warming also shifts the entire distribution of temperatures, making a formerly rare heatwave a more common occurrence. New record-breaking heat events are dramatically hotter than previous extremes. The warmer baseline temperature also exacerbates drought conditions by increasing the rate of evaporation from soil and surface water. This higher evaporation extracts moisture from the landscape more aggressively, turning meteorological droughts into agricultural and hydrological droughts. Climate change makes the conditions for previously rare and extreme events far more likely and intense, resulting in a greater number of prolonged and severe weather incidents worldwide.
The Disruption of Atmospheric Flow
The amplification of extreme weather is compounded by disruption to the high-altitude atmospheric currents that transport weather systems, most notably the Jet Stream. This fast-flowing river of air is usually powered by the large temperature contrast between the frigid Arctic and the warmer mid-latitudes. The greater the temperature difference, the faster and straighter the Jet Stream flows.
However, the Arctic region is warming two to three times faster than the global average, a phenomenon known as Arctic Amplification. This rapid warming reduces the temperature difference that drives the Jet Stream, causing it to weaken and become more unstable. A weaker Jet Stream develops larger, slower-moving north-south meanders, known as Rossby waves.
These exaggerated meanders can stall, creating atmospheric “blocking” patterns. When the Jet Stream gets stuck, it can lock a high-pressure system—a heat dome—over a region for days or weeks, leading to prolonged heat and drought. Conversely, it can lock a low-pressure system in place, causing persistent, heavy rainfall and flooding. This physical slowing of the atmospheric flow transforms extreme weather into prolonged, stagnant events. Instead of a weather system passing through quickly, it lingers, concentrating its effects and leading to unusually persistent heatwaves, cold spells, or flood events.