Scientists from the University of the Witwatersrand (Wits) have proved that, despite predictions, tropical storms were not increasing in number and that while global warming was causing frost to be less severe, late season frost was not receding as quickly as flowering was advancing, thus debunking two significant climate change myths.

However, despite these myths being disproved, the effects of climate change could still be severe as Wits studies found that tropical storms, while not increasing in number, were shifting in location and, therefore, South Africa could be at increased risk of being directly impacted by tropical cyclones within the next 40 years, while food security could be threatened by the changing frost patterns.

Wits School of Geography, Archaeology and Environmental Studies (GAES) PhD student Jennifer Fitchett explained that there had been an assumption that increasing sea surface temperatures caused by global warming were increasing the number of tropical cyclones.

However, in considering data for the south-west Indian Ocean over the past 161 years, Fitchett and co-author GAES Professor Stefan Grab confirmed the results of previous studies, which had found that there was no increase in the number of tropical cyclones and much of the perceived change in numbers was a result of improved storm detection methods.

“From 1940 [onwards], there was a huge increase in observations because of aerial reconnaissance and satellite imagery,” Fitchett said.

However, when considering where storms were taking place, Fitchett and Grab found that as the oceans had warmed, the minimum sea surface temperature necessary for a cyclone to occur, which was 26.5 °C, had been moving further south, causing storms in the south-west Indian Ocean to move further south as well.

Historically, most cyclones hit Madagascar and did not continue to Mozambique, and those which hit Mozambique developed to the north of Madagascar; however, over the past 66 years, there were seven storms which had developed south of Madagascar and hit Mozambique head-on, Fitchett said, noting that four of these seven storms occurred in the last 20 years.

“This definitely looks like the start of a trend,” she stated.

Fitchett added that South Africa was already feeling the effects of this shift with cyclones that hit southern Mozambique causing heavy rain and flooding in Limpopo.

However, she said the trend became even more concerning when it was considered that the 26.5 °C temperature line had been moving south at a rate of 0.6° latitude every decade since 1850.

“At current rates, we could see frequent serious damage in South Africa by 2050,” Fitchett pointed out.

Fitchett and Grab’s paper titled ‘A 66-year tropical cyclone record for south-east Africa: temporal trends in a global context’ reporting these findings was published in the International Journal of Climatology in February 2014.

The paper evolved from work Fitchett did in 2011, while undertaking her honours degree at Wits.

In 2012, the coauthors started the process of writing the report for publication, after which it was first submitted to the journal in July 2013 and accepted in December 2013.

Meanwhile, in a separate study, that developed from work Fitchett did during her masters degree at Wits in 2012, considering different types of citrus in two cities in Iran, Fitchett and her co-authors found that while global warming was causing fruit trees to flower as much as a month earlier than 50 years ago, which was a very rapid shift, changes in late season frost were not taking place nearly as quickly.

Before 1988, there were zero to three days between peak flowering and the last day of frost in Kerman, Iran. Since then, the number has increased to zero to 15, the study found.

“The layman’s assumption is that as temperatures get warmer, there will be less frost. But, although the severity of the frost has decreased, the last day of frost has not been receding as quickly as the advances in flowering. The result is that frost events are increasingly taking place during flowering and damaging the flowers. No flowers equals no fruit,” Fitchett explained.

Further, according to the study, at current rates it would only take 70 years before it became a certainty that frost would occur during peak flowering in Kerman, with frost already having occurred during peak flowering in 41% of the time since 1988.

“Iran is a top citrus producer but [it does] not export and we do not yet have data on whether there has been an impact on their citrus yields, [however], we think that if there has not already been a huge impact, there soon will be,” Fitchett said.

She further pointed out that South Africa also produced a lot of citrus, adding that the country had been experiencing similar climate warming to Iran.

“South African farmers are not yet recording the flowering dates of their crops which makes it hard to repeat the study locally, but the threat is of concern,” Fitchett concluded.

Fitchett and her coauthors’ paper on frost risk titled ‘Increasing frost risk associated with advanced citrus flowering dates in Kerman and Shiraz, Iran: 1960–2010’, was published in the International Journal of Biometeorology in January 2014, after having been submitted to the journal in June 2013, and accepted in Decem