Global warming is expected to result in an increase in work-related heat stress and a decrease in productivity, and to cause job and economic losses. Concerns over workplace heat exposure were first raised in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [1] and received a stronger focus in the Fifth Assessment Report [2]. The IPCC’s Fifth Assessment Report confirmed that labour productivity impacts could result in output reductions in affected sectors exceeding 20% during the second half of the century–the global economic cost of reduced productivity may be more than 2 trillion USD by 2030 [2]. An increase in heat stress resulting from global warming is projected to lead to global productivity losses equivalent to 80 million full-time jobs in the year 2030, according to a new report from the International Labour Organization [3].

Regional and temporal variability of climate is the major determinant of agricultural production in Ethiopia. Mean annual temperature has risen by 1.3˚C between 1960 and 2006, an average rate of 0.28˚C per decade [4]. Daily temperature observations show an increasing frequency of both hot days and hot nights. Climate models suggest that Ethiopia will see further warming in all seasons of between 0.7˚C and 2.3˚C by the 2020^s and of between 1.4˚C and 2.9˚C by the 2050s [4] [5]. An increase in rainfall variability is also predicted, with a rising frequency of both extreme flooding and droughts that could seriously affect agricultural production. Agricultural production and productivity including the floriculture sector are related to the performance of improved and adaptable technologies, which are destined for a particular environmental condition [6] [7].

In Ethiopia, commercial flower production is practiced mainly under greenhouse structures. Given the diversity of climatic conditions and altitudes in Ethiopia, different types of flower species and varieties are grown and each type of flower has different optimal conditions varying by light intensity, light exposure, soil acidity, water needs and temperature amongst other factors. Under greenhouses, for most commercial varieties, the best quality of flower shoots, in terms of stem length, diameter of leaf area and flower bud size, is obtained at 28˚C. As temperature increases, the periods from cut back to flowering became shorter; stem became shorter, diameter and leaf area smaller, flower weight decreases and adjoins with fewer and smaller petals [8]. The most important environmental parameters that need to be controlled for optimal greenhouse climate are temperature, light, relative humidity, and carbon dioxide (CO₂). Temperature is the most important single parameter as it has a significant role in plant growth and development. The optimal temperature depends on the plant species grown and desired level of photosynthetic activity.

The Ethiopian flower industry is growing fast with successful diversification of export products (Figure 1). The country is now the second-largest flower exporter in Africa, with 84 active flower farms on 1426 hectares [9]. The floriculture industry has also had a huge impact on Ethiopia’s economy and society; most significantly on job creation. The area cultivated is expected to grow to 3000 hectares in the coming five years and the revenue is projected to increase to $550 million [10]. Cut-flower production is a labour-intensive activity, since few tasks can be mechanized, making labour costs a significant factor. The workforce in the flower industry is predominantly female, as more than 80% of workers are female [8]. Occupational heat stress is expected to be a significant problem in flower greenhouses in Ethiopia. Excessive heat while working, generally at temperatures above 35˚ Celsius, creates occupational health risks and reduces work capacity and labour productivity [11].

Given the diversity of climatic conditions and altitudes in Ethiopia, different basic types of rose varieties are grown in greenhouse structures and each type of flower has different optimal conditions varying by light intensity, light exposure, soil acidity, water needs and temperature amongst other factors. For most commercial varieties, the best quality of flower shoots, in terms of stem length, diameter of leaf area and flower bud size, is obtained at 28˚C. As temperature increases, the periods from cutting to flowering became shorter; stems became shorter, diameter and leaf area smaller, flower weight decreases and adjoins with fewer and smaller petals [8]. Temperature can also affect plant quality. Too high temperature reduces plant growth, eventually resulting in plant wilting and death whereas too low temperature limits plant growth.

Occupational heat stress (excessive workplace heat) is a well-known occupational health and productivity danger in the agriculture sector [12] [13]. Excessive heat (generally when WBGT exceeds 26˚C) while working creates occupational health risks and reduces work capacity and labour productivity [14]. Exposure to hot environments and extreme heat can result in illnesses, including heat stroke, heat exhaustion, heat syncope, heat cramps, and heat rashes, or death [15]. Maintaining a core body temperature close to 37˚C is essential for health and work efficiency, and excessive sweating as a result of high heat exposure while working creates a risk of dehydration [3]. Studies have shown that workers often only replace approximately half to two-thirds of the fluids lost through sweating at work when fluid is freely available. Excessive body temperature and/or dehydration causes “heat exhaustion”, slower work, more mistakes while working, clinical heat effects [16] and increased risk of accidental injuries [17]. Heat stroke, which can be fatal in the absence of swift, effective treatment, is the most serious health risk posed by heat stress.

The International Organization for Standardization (ISO) has adopted assessment methods for the risk of heat stress [18]. The most commonly used is the wet-bulb globe temperature (WBGT) index, which is calculated by measuring the natural wet-bulb temperature, the global temperature and the air temperature to estimate the effects of temperature, humidity, wind speed (wind chill) and visible and infrared radiation (usual sunlight) on humans.

The main objective of this paper is to present the findings of measured occupational heat stress exposure and perceived impacts of heat exposure on the health and productivity of workers in six different floriculture greenhouses in Ethiopia representing three different agroecologies and products.

Occupational heat stress and workers’ perceptions of the impact of heat on their health and productivity were studied in 6 different floriculture greenhouses representing three different agroecologies and two production systems (Table 1). Greenhouses from around three cities in Ethiopia (Holetta, DebreZeit and Ziway representing highland, midland and lowland agro-ecologies, respectively) were selected in consultation with the Ethiopian Horticulture Producers and Exporters Association (EHPEA). Farms that had been functional for the last 12 months prior to the study were eligible for the study. The selection of two farms from each agroecology was considered to cover diverse working conditions based on consultations with the Ethiopian Horticulture Producers and Exporters Association (EHPEA). Greenhouse structures and different production systems were also compared in terms of heat exposure.

The study used Wet Bulb Globe Temperature (WBGT) to capture heat exposure and a questionnaire survey to capture perceptions on heat exposures, symptoms of potential health impacts, productivity losses and coping mechanisms (Figure 2). Quantitative data on heat stress exposure were collected using the Wet Bulb Globe Temperature (WBGT, Ques Temp 34WI, USA) placed in each of the six greenhouses to capture the heat exposure during hotter (May) and cooler seasons (November) following the Organization of International Standards (ISO) screening method for evaluating heat stress [18]. WBGTs were positioned in the six greenhouses and were mounted at a height of 1.1 m using a tripod stand in a representative location without any obstruction. In every agro-ecology, one additional WBGT was mounted outside the greenhouses for control.