SLU news

More and happier pathogens in warmer Nordic countries

Published: 04 April 2024
Wheat with fungal disease. Photo.

The majority of all known pathogens to global food production will thrive and reproduce faster in a warmer climate. Such generalizations are, however, not necessarily practically useful. A new report from SMHI and SLU estimates at a geographically higher resolution how 80 known plant pathogens are affected by climate change.

A changing Nordic climate will be beneficial to the growth of most plants, but also to growth of their pathogens. As far as crops are concerned, this increase is based on at least three factors – higher temperatures, a longer growing season, and higher atmospheric CO2 levels. All scenarios agree that this will happen – any uncertainty comes down to how large the changes will eventually be.

Future scenarios

The IPCC (Intergovernmental Panel on Climate Change) makes several different assumptions regarding the future emissions of greenhouse gases (so called RCPs).

RCP2.6 is considered very stringent and requires that CO2 emissions start decreasing immediately. Global temperature increase from pre-industrial levels is today at 1.1 degrees C, and is, following RCP2.6, estimated to keep below 2 degrees by 2100. Considering that emissions are still increasing, it is highly unlikely that this scenario will occur.

RCP4.5 is an intermediate trajectory which requires that emissions peak by 2040 and have shrunk by half by 2100. Temperature increase will stabilize at 2-3 degrees. This is commonly viewed as a plausible development. It does, however, demand that we do start to decrease the emissions of greenhouse gases. So far, they have been increasing yearly. 

RCP8.5 is the most extreme scenario, and assumes that emissions keep increasing throughout the 21th century. This would increase global mean temperatures by ca 5 degrees. Most assessors consider this implausible, partly due to the limited abundance of fossil fuels.

Higher latitudes are assumed to be more affected. For example, mean temperatures in Sweden has increased by 1.9 degrees since the end of the 19th century, i.e. almost twice the global mean, and the changes will affect northern and southern Sweden differently. According to RCP2.6, the growing season in southern Sweden will be prolonged by 20-40 days by the end of the century, and by 10-20 days in the north. The same numbers for RCP8.5 is 90-100 days and 50-60, respectively.

Benefited pathogens

This is why gross production of food may be expected to increase, but it is uncertain how large the net effect will be. When a plant thrives, its pathogens do as well. A warmer climate will make most microorganisms more active, and as the growing season lengthens, they will also be active for a larger part of the year. At the same time, the geographic area in which they thrive will expand.

But as true as this is, it is still too vague and imprecise information to be practically useful for anything but alarm bells. However, in a fresh study by SMHI and SLU, a first step is taken to sharpen this forecast for the future, by trying to estimate the fate of individual pathogens in a warmer climate.

The scientists used climate data from SMHI to estimate the temperature development up until the year 2100, for each 12,5 km2 in a grid covering the Nordic and Baltic countries. This was done for each of the three emission scenarios. The temperatures were subsequently compared to growth temperatures for 80 known plant pathogens. The result was partly a composite image of how pathogen species richness may develop locally in the future, and partly individual estimations of the fate of each microorganism.

Increased species richness

For each individual pathogen, the projected development varied somewhat, but nearly all were estimated to do better the warmer it gets. Most follow the same pattern as the common wheat pathogen Fusarium graminearum. The Swedish climate in Svealand and Götaland (southern third of the country) is today fairly beneficial for this fungus in July, but far from optimal in June and August. Following RCP4.5, May through September will be beneficial, and in July and August, Svealand and Götaland will provide nearly optimal growing temperatures. Almost the entire country, apart from the alpine range, will experience very beneficial conditions for Fusarium graminearum in July. This was true for most of the 80 pathogens.

The species richness of the pathogens is also expected to increase. The numbers vary greatly locally, but on average, the temperatures in northern Norrland today is beneficial to fewer than 20 of the tested pathogens. With RCP4.5, the number increases to almost 40 species, and with RCP8.5 to 50. In southern Sweden, the increase is from 45 today, to 60 respective almost 70 benefited species.


The common trend for these 80 pathogens is that most will thrive in a warmer climate.

– The question is not IF problems with pathogens in food production will increase, but how large they will become. Thus, it is in our own absolute interest in keep global warming at the lowest level possible, says SLU researcher Anna Berlin.

Written by Mårten Lind.


The project was financed by national research and education funds from the Swedish Board of Agriculture.