Why do heat waves cause record temperatures in Europe and will they reach Estonia?

European heat waves are not random phenomena but result from the combined effect of multiple natural and human-caused factors. The jet stream, Saharan desert air, a warming Mediterranean Sea, and climate change all play a role. Meteorologists warn that records are set by the convergence of patterns recently considered unlikely.

When thermometers in Europe rise above 40 degrees, the culprit may seem obvious at first glance. In reality, however, a European heat wave is the result of a complex atmospheric puzzle involving multiple natural and human-induced phenomena working in concert.

Jet stream and Saharan dry air

One of the primary shapers of heat waves is the jet stream that meanders through the troposphere-a fast-moving system of wind bands high in the atmosphere that influences weather patterns across Europe. When the jet stream becomes more wave-like or weakens, high-pressure systems can stall for weeks, allowing solar radiation to accumulate on the ground unimpeded.

Saharan desert air is another crucial link in this chain. A dry and hot air mass moves from North Africa towards southern Europe, further raising temperatures and reducing the likelihood of cloud formation. Combined with a stationary high-pressure system, this creates conditions where heat does not retreat over days but over weeks.

El Niño and the Mediterranean's role

Meteorologists have also highlighted the impact of the El Niño phenomenon. El Niño is a periodic deviation in the Pacific Ocean's warm water current that affects weather patterns across the globe, including in Europe. Under warmer sea surface temperature conditions, evaporation from the Mediterranean also increases, adding moisture and energy to Europe's climate and deepening the likelihood of extreme weather events.

The Mediterranean itself has warmed significantly over recent decades, becoming in turn an amplifier of heat waves. The warm sea imparts additional heat to moving air masses, which they then carry northward into northern Europe.

Climate change raises the bar

Human-caused climate change is a factor that meteorologists can no longer afford to ignore. The rising concentration of greenhouse gases in the atmosphere is raising global average temperatures, making temperature records that once seemed unprecedented increasingly likely. Patterns that were recently considered extraordinarily rare are now occurring far more frequently.

The urban heat island effect deepens the situation further. Dense buildings, asphalt, and sparse vegetation make cities substantially warmer compared to rural areas, meaning that city dwellers suffer disproportionately during heat waves.

When will the heat reach Estonia?

Estonia is geographically located in a region where southern European heat waves typically arrive with a delay and in diminished form. Nevertheless, in recent decades, the frequency and intensity of heat waves in Estonia have also increased. If a high-pressure system shifts far enough northward, heat can reach the Baltics for multi-day periods during which temperatures exceed 30 degrees.

Meteorologists stress that no specific heat wave arrival in Estonia can be predicted far in advance, but against the backdrop of climate change, this is becoming an increasingly likely scenario in our region as well.