It is an interesting study, methodologically correct and well developed by a group of researchers who in some cases have worked extensively in the field of global climate dynamics and simulation. The techniques are consistent and the data used adequate, with clear and robust results and which constitute a notable advance, since this approach to abrupt changes is novel. 

More than changes in mean temperature and variable trends, the most relevant information because of its immediacy and potential effect in terms of impacts on ecosystems and human health are those changes that are related to the behavior of climatic extremes, i.e., phases of droughts, floods, heat waves or cold drops, for example.  

This study clearly shows with high resolution observational data how, both globally and regionally, more than 60% of all regions studied have experienced clear and drastic changes in terms of increased frequency in the transition of these weather extremes within a few days. That is, cold phases transition from warm days more often and with greater intensity, and with less time between extremes. This fact can have clear and more pronounced effects on the survival of ecosystems, for example (think, for example, of the successive droughts in regions of Brazil in recent years, which caused greater tree mortality than much more intense individual events). It seems clear that vegetation, for example, is less adapted to withstand repeated dry or wet events than a single more intense one, because vegetation has less time to recover. 

Similarly, negative effects on human health are expected, although the study makes only rough inferences about this, but clearly this is an area that will deserve more attention in the future. 

The limitations of the study basically relate to simulations of extremes in future scenarios, for which climate models are not as well prepared as they are to simulate the average behavior of the climate. In this sense, using CMIP6 simulations to infer daily changes on decadal scales seems to me to entail considerable uncertainties that perhaps should have been highlighted in this study. Direct effects on human health are also not studied with the detail and approximation that would be required, although I understand that they are left for later studies.  

In summary, an interesting study that provides clear information on an apparent discrepancy with respect to the effects of global warming, since this increase in frequency may be accompanied by a greater impact not only in warm phases (to be expected), but also associated with cold extremes, which is new.

The increase in the frequency of rapid transitions between situations with opposite extremes of temperature and precipitation in a context of global warming has been recently discussed. In the case of precipitation, the increase in the frequency in which drought situations end with intense rainfall and vice versa has already been studied in other studies. In the case of this work on temperature, it has been shown that since 1961 the frequency, intensity and speed of rapid transitions between a situation of extreme high temperature and another of extreme low temperature and vice versa has increased. This behavior has been demonstrated over more than 60 % of the regions studied, with Western Europe being one of the most affected regions. The authors have also estimated how much this effect will grow under high emissions scenarios during the 21st century and the population that will potentially be affected.  

This increase in abrupt changes between temperature extremes constitutes an additional challenge to adaptation, since the effects are clearly more negative when warming also shows strong oscillations between temperature extremes. Particularly affected may be the ecosystems and sectors most vulnerable to these strong temperature swings that leave very little room for adaptation. An example of this may be more frequent crop losses due to frost after a warm period that has resulted in early flowering or fruiting.   

From the point of view of climate change communication, these sharp swings between temperature extremes that are superimposed on the general warming trend can be used to cast doubt on climate change, when in fact it is an additional negative effect that is superimposed on the background warming trend.

“The weather is crazy” is a phrase that almost all of us have uttered when we go abruptly from hot to cold, or vice versa. The new study scientifically demonstrates how, indeed, the weather is getting crazier and crazier, and that climate change is behind the increasing craziness.  

When we talk about climate change, we are not just referring to it being warmer on average, but to a more general destabilization of the climate system: more heat waves (and cold waves in some cases), more extreme events and greater climate volatility (or increasingly crazy weather). This year has been a good example of the latter, as we have seen rapid swings between spring and winter temperatures. This climate volatility is a process that has not received much attention until now and the published study is among the first to address the influence of climate change on this phenomenon at a global level.

The study shows how climate volatility will increase as a consequence of climate change. The consequences for agriculture can be dramatic, because a few days of early warmth in winter can favor the flowering of many species which, after the return of freezing temperatures a few days later, can destroy that year's crop. These sudden temperature changes also have serious effects on infrastructure, because of the rapid expansion and contraction in response to these temperature changes. Human health can also suffer from these sudden changes in temperature, especially in the most vulnerable groups.