Not warming to climate change

The latest climate change reports from the Intergovernmental Panel on Climate Change (IPCC) reinforce the urgent need to reduce global greenhouse gas emissions as well as to adapt to the impacts of climate change. Michelle Sutton finds that the news is mixed for New Zealand’s agricultural sector.

The fifth round of IPCC reports began in September 2013 with an update on the latest science (known as the Working Group I report). This report restated that warming of the climate system was unequivocal and that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid 20th century.

At the start of 2014, the IPCC released a second report discussing the likely impacts of a changing climate, how people are adapting and may adapt, and the vulnerability of people, environments and ecosystems to climate change (known as the Working Group II report).

This report included a chapter that focuses on Australasia. The New Zealand lead authors of the Australasian chapter are NIWA climate scientist Dr Andrew Tait, AgResearch scientist Dr Paul Newton and New Zealand Agricultural Greenhouse Gas Research Centre scientist Dr Andy Reisinger.

Dr Tait, who hopes the report will be “a wake-up call”, says the world’s climate will continue to be affected by ever-increasing concentrations of carbon dioxide and other greenhouse gases in the atmosphere.

“New Zealand is projected to get hotter, have heavier rainfalls and experience more days when the fire risk is extreme.”

Drought is expected to increase in frequency, even in Southland and Otago, and flooding is predicted to more frequently impact much of New Zealand’s low-lying areas, as heavy rainfall events are projected to increase in intensity.

‘’The big ones will be even bigger. A present-day 1-in-50-year rainfall could be more like a 1-in-20-year event by the end of the century,’’ Tait says.

In fact, the new IPCC work suggests many of the impacts are already being experienced by the agricultural sector.

Droughts, floods and changing weather patterns are an increasing problem for farmers around the world, and the consequences fit with patterns predicted in the last IPCC report in 2007.

It may not be all bad news. Recent studies have indicated that warmer temperatures may mean strong spring growth in cooler parts of New Zealand, and better yields and new crop types in traditional agricultural areas.

Productivity losses from warming may be offset by the enhanced fertilisation effect of increased atmospheric carbon dioxide. This was suggested by a 2013 report from the Ministry for Primary Industries on New Zealand’s agricultural adaptation to climate change, Four Degrees of Global Warming, co-authored by NIWA scientists. This could boost productivity by an estimated 30 to 40 per cent on average, depending on the climate change scenario, as long as nutrients and water are not limiting.

But globally, scientists are becoming more ambivalent about the impact of climate change on agriculture. There are some indications from studies overseas that rising carbon dioxide levels could reduce the effectiveness of herbicides, encourage pests and plant disease, and may even reduce the protein level in plants.

A literature summary published in the journal Agricultural Economics at the end of last year found scientists studying the effect on agriculture had experienced “a transition from relative optimism to significant pessimism”.

Professor Tim Naish, Director of the Antarctic Research Centre, Victoria University of Wellington, worries about whether New Zealand is ready to adapt. He warns, “New Zealand is under-prepared and faces a significant ‘adaptation deficit’ in the context of the projected impacts and risks from global average warming of +2 to 4°C by the end of the century.”

One of the benefits of the new IPCC report, according to Dr Tait, is that it stresses the importance of adaptation. He says it “is a chance to restate and re-emphasise the climate change vulnerability and adaptation issues that we face”.

Farm management skills are also central to the quality of adaptation. The IPCC chapter on Australasia cites studies that measured the ability to respond to projected climate-change-driven variations in seasonal pasture growth. In Hawke’s Bay, changes in stock numbers and the timing of grazing were techniques used to maintain farm income in the face of variable forage supply, but not over the longer term. In Southland and Waikato, projected increases in early spring pasture growth may negatively affect pasture quality, yet, if quality is preserved, animal production could be maintained or increased.

Many adaptations are already in play on farms today, such as new planting and harvesting dates to account for seasonal changes, and different crop selections to account for warmer temperatures and pests.

The IPCC’s Fifth Assessment report says people may soon see some very surprising land-use changes, such as the introduction of crops and fruits in regions that had never considered them previously.

Studies have indicated that crops such as soybeans, rice and sorghum could be grown here if the climate gets warmer and wetter, and fruits such as avocado and a wider range of citrus could be grown in more areas.

Modelling cited in the recent Working Group II report, for example, also suggests that good choices of cultivars and sowing dates could increase our wheat yields under climate change.

At the same time, problems may emerge for existing agriculture. A 2012 technical paper from the Ministry for Primary Industries expected a range of changes in crop diseases and pests ("Climate change impacts on plant diseases affecting New Zealand horticulture"). For example, apple black spot may thrive, but grapevine downy mildew would not increase significantly. The risk of the dreaded kiwifruit bacterial canker known as Psa would decrease in some regions like Northland but not change in places like Nelson.

This suggests subtle regional shifts in agricultural production over time as the effects are felt differently across the range of agriculture.

An intriguing problem raised in the IPCC report is that New Zealand may be so good at on-farm adaptation that we actually delay the degree of transformation response required by the nation as a whole. Better crop and stock management techniques may enable us to maintain production against the disease, pest and growth impacts of climate change. But this adaptation may mask the extent to which certain types of farming are no longer viable in regions.

So we may put off the most difficult adaptation: wholesale shifting of locations for entire industries, or the dissolution of industries and initiation of new ones.

When it finally occurs, the transformation may be all the more jarring. New Zealanders who have been surprised by the scale of economically driven land transformations in the past two decades may recoil at the scope of environmentally driven transformation.

The major message in the latest IPCC material is that incremental adaptation is happening right now, almost imperceptibly. Yet science is clearly identifying specific climate impacts on agriculture – impacts that should be responded to consciously with organised and large-scale adaptation, and even displacement, of our traditional agricultural sectors.


Don’t wait

New Zealand’s agricultural sector needs to prepare for climate change, rather than wait until the implications hit home, warns a climate and agriculture researcher.

The worst thing farmers can do is ignore climate change just because the implications are not fully understood, says Andy Reisinger, a coordinating lead author for the IPCC Fifth Assessment report. He is also Deputy Director (International) of the New Zealand Agricultural Greenhouse Gas Research Centre.

Reisinger likens the need for some adaptation actions to putting on a seat belt – it’s a prudent action even though you don’t expect to actually have an accident.

“You don’t want to try to put on a seat belt when you realise you are going to crash – it’s too late by then, and the same is true for dealing with climate change,” he says.

Farmers and agriculture land owners need to think through their options now so they can be prepared for a variety of outcomes in the future.

“There are still many uncertainties about what climate change will mean for farmers in New Zealand, with issues such as the amount of rainfall change in some New Zealand regions, changes in pests and diseases, effect of higher carbon dioxide concentrations and, not the least, policy responses. It’s important to be prepared for as many of these scenarios as possible to safeguard your land, income and future.”

In the short term, farmers could best prepare by being able to survive greater variability in climate, feed supply and income. Simply put, higher temperatures and shifting rainfall patterns, with a broad trend towards more droughts in many regions, would impact on food supply, productivity and animal health. Some of those changes are expected to be positive for parts of the country, but greater variability would also imply more extremes in returns at the farm gate.

However, the full implications of climate change for New Zealand farmers needed to be understood in the international context.

“Looking at climate change’s impact on New Zealand alone, it would be easy to lose sight of the international situation and how global changes flow back onto New Zealand farmers,” Reisinger said.

The impact of climate change on other countries is expected to increase commodity prices, but also influence international markets more generally; as an export-dependent nation, such changes could be critical in shaping land use and strategies to adapt agriculture in New Zealand.


New Zealand impacts at a glance


Warming; with rising snow lines, more frequent hot extremes, less frequent cold extremes and increasing extreme rainfall related to flood risk. Annual average rainfall is expected to decrease in the north-east South Island and northern and eastern North Island, and to increase elsewhere.

Water resources

Increased water runoff in the west and south of the South Island, and reduced runoff in the north east of the South Island and the east and north of the North Island. Annual flows of eastward rivers with headwaters in the Southern Alps (e.g., Clutha, Waimakariri, Rangitata) will increase in response to higher alpine precipitation, especially in winter and spring.


Flood risk is projected to increase due to more intense extreme rainfall events driven by a warmer and wetter atmosphere. The 50-year and 100-year flood peaks for rivers in many places will increase (large variation between climate models and greenhouse gas emissions scenarios), with a corresponding decrease in return periods.


Climate change is expected to increase the number of days with very high and extreme fire weather in many, in particular eastern and northern, parts of New Zealand. Fire season length will be extended in many already high-risk areas, and so will reduce opportunities for controlled burning.


Upper-end projections for New Zealand

A 2013 report from the Ministry for Primary Industries, co-authored by NIWA scientists, Four Degrees of Global Warming, estimated how New Zealand weather might change under a scenario where the global temperature increased by an average of four degrees from pre-industrial times.

It suggested that the greatest temperature rises are likely to be in inland and eastern areas of New Zealand, with the biggest rises in winter and the least in summer. Some areas, such as eastern South Island, may warm by approximately 5.3 degrees.

Frost will become a rare sight, with almost none in most lowland sites in the North Island and none in South Island coastal regions like Marlborough, Canterbury and Southland, the report says.

Consequently, growing-degree days, or the number of growing days it takes for plants and pasture to reach maturity, will improve significantly, by between 50 and 100 per cent in most locations.

This would lengthen some growing seasons considerably, and ease temperature limitations for some crops. However, it would also reduce winter chilling for crops such as pipfruit and stonefruit and may allow some pest species to survive through winter.

If temperatures are four degrees warmer, then the intensity of heavy rainfall events is projected to increase by around 30 per cent. Increases of between 50mm and 150mm per day are expected in many locations and, if expected stronger westerlies increase uplift and rainfall over the Southern Alps, these changes could be even larger.

Average annual water discharge is projected to increase in all six catchments analysed by the report: the Clutha, Ahuriri, Waimakariri, Rangitata, Ashley and Rangitaiki.

While increases in extreme maximum rainfall volumes will lead to higher flood flows, more and longer dry spells may also see lower low flows. This means less water will be available during times of highest irrigation demand. River flows are expected to alter seasonally as less snow accumulates on the ranges in winter and, consequently, less melts over summer and spring.

Even though growing seasons may lengthen, temperature increases of this magnitude are likely to result in a decline in pasture production for both sheep/beef and dairy, due to extreme warming, and summers with more days above the heat stress threshold of dairy cattle will become more common.

Northland and northern Waikato may experience more heat load and, without adaptation, heat stress could undermine production, reproduction and animal welfare. Adaptations include shifting to more heat-tolerant breeds, milking only in cooler months and providing more shade or indoor cooling for stock.

Farmer, Angela Hunt surveys a dry dam which is normally used to supply stock with drinking water, Wairarapa. [Dave Allen]