Basics of climate change: Q&A with Dr. Andrew Tait
Dr Andrew Tait, NIWA scientists briefing councillors on an update on global warming impacts for Hawke's Bay. Photo / Supplied Ahead of next week's UN climate change conference in Paris, the Herald's science reporter Jamie Morton is talking to a range of experts on climate-related issues. Here he talks to Dr Andrew Tait, principal climate scientist at the National Institute of Water and Atmosphere, about the basics of climate change. Q. What are the key components that cause anthropogenic or human-driven climate change, and how do they interact to elevate average temperatures? A. The burning of fossil fuels - coal, oil and natural gas - adds CO2 into the atmosphere that would otherwise have remained sequestered away deep underground. While the additional carbon is naturally cycled between the atmosphere, soils, ocean and biosphere, there has been a distinct increase in the amount of CO2 in the atmosphere over the last 50 years since measurements began. This increase can be directly attributed to anthropogenic activities; predominantly the burning of fossil fuels, but also deforestation. Atmospheric concentration of other greenhouse gases such as methane and nitrous oxide have also been increasing over the last several decades, due mostly to the intensification of agricultural practices around the globe. These increases in greenhouse gases have led to an increase in global temperatures, as the gases are very efficient at absorbing and re-emitting some of Earth's heat energy that would otherwise be radiated away to space. Q. In New Zealand, what amount of temperature rise have we seen, and over what period, that can be attributed to climate change? A. Over the last 100 years, the average temperature for New Zealand has increased by approximately 1C. Most of this increase can be attributed to anthropogenic increases in greenhouse gas concentrations in the atmosphere. Q. Under the latest UN IPCC projections, what projections have been made for future temperature rise? A. The amount of temperature increase over the coming century is dependent upon the future concentration pathways of greenhouse gases. A selection of "representative concentration pathways (RCPs)" has been defined to represent future greenhouse gas concentrations associated with low, middle and high emissions of the gases. The RCPs are used in global climate models to determine the climate response to the amount of radiative forcing. Q. Along with these projections, the report found it was "extremely likely" that human influence was the dominant cause of observed warming since 1950. What was it about this report that made it the most robust yet on climate change and how many scientists were involved it its publication? A. The IPCC's Fifth Assessment Report (AR5) presents an assessment of the latest published literature on climate change. Over the last few decades, more and more research on the physics of climate change and on the causes and effects of climate change has been performed, to the point where the global literature is now very well advanced. While still more research is needed, particularly on the impacts of climate change, many of the conclusions in AR5 have been made with "very high confidence" due to this great wealth of scientific knowledge. More than 830 Authors and review editors from over 80 countries were selected to form the author teams that produced the IPCC AR5. They in turn drew on the work of more than 1000 contributing authors and about 2000 expert reviewers who provided more than 140,000 review comments. Q. Still, what key uncertainties remain around climate modelling today? A. The principal uncertainty associated with projections of climate change is what the greenhouse gas concentration pathway will be over the next century and beyond. This is a direct function of the rate and amount of global greenhouse gas emissions, which is a huge unknown. The global climate models that are used to project future climate based on RCPs can still be further refined to better approximate the Earth climate-ocean-biosphere "system", with the most significant improvements likely to come from improved representation of clouds and the effects they have on the energy and water balance of the planet. Q. In New Zealand, what broad atmospheric and environmental impacts from climate change, including extreme weather events, are we likely to see before 2050 and how will these differ around the country? A. This is an area of active research, with the amount of change directly related to greenhouse gas concentration levels in the atmosphere. Generally for New Zealand, we expect to see a continued gradual increase in air and sea temperature and sea level and acidification, slightly wetter conditions in the south and west and drier in the east and north of the country (particularly in winter), and a gradual increase in the number of heavy rainfalls (potentially leading to floods) and droughts (potentially leading to wildfires). There is also likely to be a decrease in frosts and in increase in hot, dry days. Q. By 2100, under mid-range projections, what will be some of the biggest transformations that have happened? A. For New Zealand, we will see the significant impacts associated with sea level rise, potentially up to 1m above present day levels. This will likely lead to transformations in our coastal environment and infrastructure - either with major protection schemes or with retreat options, or both. Q. What will these impacts likely mean for primary industries in New Zealand? A. Land-based primary industries in New Zealand will need to adapt to the changes in water availability and temperature by modifying management practices and land use. Similarly, inshore and offshore-based primary industries will need to adapt to changes in water temperature, sediment contamination and acidification. Fortunately, primary industries in New Zealand are adept at adapting to an already quite variable climate, as well as other stressors. In saying this, some future climate changes may mean some areas of New Zealand may become very difficult to farm using traditional systems. Q. For New Zealand, what direct and local impacts might we see from the acidification of oceans? A. We know the pH of the ocean around New Zealand is decreasing from long term measurements in subantarctic water off Dunedin. The impacts of this acidification are currently unclear but this is an active area of research, with a new four-year government-funded project on impacts in coastal waters where some of the more immediate effects may occur. Organisms that produce carbonate shells and structures are sensitive to lower pH, particularly at the larval stage, and this may impact future populations and availability of kaimoana such as paua and kina. Shellfish aquaculture on the north-west US coast has already been detrimentally affected by ocean acidification, and we are examining the potential impacts on greenshell mussels in New Zealand. The penetration of additional carbon dioxide into the deep ocean may reduce the distribution of cold water corals, which provide homes for fish larvae and invertebrates. However there may also be "winners", with some marine algae (phytoplankton, seaweeds, seagrasses) benefitting from the increase in dissolved carbon dioxide. Overall, there are documented impacts on a variety of different organisms, from bacteria to fish, but the complexity of the interactions between biology and seawater chemistry makes it currently difficult to predict how New Zealand marine ecosystems will change. Q. Under presently projected scenarios, how might New Zealand fare compared to most other nations in the world? Is there anything to suggest our experience will be potentially less damaging than that of most others? A. New Zealand is likely to fare better than many other nations as we already have a high capacity to adapt to climate change, compared with poorer nations, plus due to our maritime location we will not be as detrimentally affected by impacts such as drought, compared with continental areas of the world. New Zealand air temperature is expected to warm about 20 per cent slower than the global air temperature over the long term. Nations with significant areas of low-lying land, such as Pacific atolls and countries with highly populated river deltas, will also have greater exposure to sea level rise than we do in New Zealand. However, we are particularly exposed to climate change increasing extreme rainfall, due to increased moisture carried in air from the sub-tropics that encounters our mountainous terrain. Some of New Zealand's iconic natural eco-systems may also struggle to adapt to the relatively rapid changes in rainfall and temperature that occur with climate change. Crews were called to the scene around 8.20pm.