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A heat wave has hit Israel and several other places around the world, including northwestern Europe and some areas of the United States. On the surface, there's nothing surprising about a heat wave in the summer. But in recent years, any extreme weather phenomenon is almost automatically connected to the broader problem of global warming and greenhouse gas emissions.

Climate researchers like Daniel Rosenfeld, a professor at the Hebrew University of Jerusalem, monitor weather patterns over extended periods and attempt to determine when a spell of hot weather is more than a heat wave.

Danny Rosenfeld, is the world experiencing an unusual heat wave?

In Israel's case, we're talking about a heat wave that is more or less typical for the season. The temperatures are higher than average, but there is no record-breaking heat. In some areas of the United States and Europe, we are talking about a very serious heat wave. In Germany, the temperature reached 38 degrees, which is only two degrees less than hottest temperature measured, in 2003, a year that will live in infamy after many people died because of the heat. Spain is also experiencing particularly high temperatures, up to 39 degrees, but in Spain the summer temperatures generally rise above 30 degrees.

So is this just another summer, but with a few particularly hot days?

To a certain extent yes, but there is a phenomenon that can explain the extreme heat in areas such as Europe, at least partially, and we really do not understand it. It turns out that this year, and in general for the last few years, the ice layer of the Arctic Ocean has been disappearing at a quicker pace. This ice layer reflected some of the sun's rays, helping to moderate the weather during the summer. If it disappears at a quicker pace, its ability to moderate the heat also decreases.

What we have trouble understanding is that the disappearance rate is faster than what it should be according to the calculations of scientists who attempted to determine how the ice would disappear in the wake of the greenhouse gas emissions that cause global warming. Usually, we are told that we are being hysterical with our warnings about climate change, but it is possible that we have not been stern enough.

What about the heat wave here?

We are affected by hot air that reaches the Mediterranean Sea and, because of the contact with the water, it is moderated a bit; this happens in the lower strata [of the atmosphere]. However, in the higher strata we receive hotter air that arrives from tropical regions and elsewhere. The contact between these strata is the point where the hot and humid air on the coast meets the dry air of the mountains. All of this looks like it's going to continue for the next few days, at the current level of heat.

Taking the longer-term view, to what extent has global warming affected summertime temperatures?

There is a trend of global warming around the world. In the summer, it is already being felt in different areas, and that corresponds to the scientists' calculations. Here it is reflected in higher average temperatures and more heat waves in the summer. By contrast, here and in the eastern Mediterranean as a whole, the winter remains fairly stable. In other part of the world, though, there has also been a warming trend in the winter. An example of this is the countries of the western Mediterranean, such as Italy and Spain, where over the last 50 years there has been an increase of more than one degree in the average winter temperature.

One part of the world that has been attracting a lot of attention over the last few weeks is South Africa, where we saw people wearing coats and getting drenched in the rain. What kind of weather were they having over there during the World Cup?

In the Cape Town area there was Mediterranean weather, but the opposite of what is happening here. For us, it's the height of the summer and for them it's the height of the winter. As fate would have it, there were several cold waves there, and that's why we saw people wearing coats and experiencing particularly cold weather, and it was also raining. However, in the Johannesburg area, the weather was comparable to the wintertime weather in the Sinai Peninsula. There was a large gap between the daytime and nighttime temperatures, and while it was hot during the day, at night it was really cold and there were several times where there was a frost.

Getting back to Israel, where's the best place to go while the weather's hot? Of course, the beaches in Israel are very pleasant at such times. There's a breeze, the water temperature is comfortable and there are waves. On the other hand, in places such as Turkey and Greece, there is a dry, hot wind on the shores and the water is also colder. These days, I wouldn't trade Jerusalem for any place else because in the evening the sea breeze reaches here too. In Europe, the situation is terrible because it is very hot there and the temperature highs are even higher than in Israel, and the daylight hours are longer. They, of course, are not set up for it, as far as air conditioning is concerned. The sea might have been perfect, if only it wasn't full of jellyfish. Don't climatologists have a solution for that yet?

I am afraid that is a little beyond my area of expertise. Unfortunately, I really do not have a remedy for that.