Climate expert Kevin E Trenberth runs his eye over the Government’s emissions reduction plan, putting it in a big picture context, and giving it a qualified thumbs up

As a climate scientist who worked in the US for 42 years, I have a more global view of climate issues than most.  I have been prominent in the Intergovernmental Panel on Climate Change (IPCC) assessments and the World Climate Research Programme. Now I am back in New Zealand, I have a strong interest in how NZ deals with climate change, and there is much that could be and needs to be done.  Which leads us to the Government’s Emissions Reduction Plan, released on Monday.

The new plan is to be highly commended in several areas. There is excellent planning for improving emissions from transport, including buses, cars, trucks and encouraging cycling.  There are initiatives around huge gains that can be made through increased energy efficiency, both in industry and in housing, and these are to be applauded. Other gains have multiple benefits by managing waste and cutting methane emissions from landfills. 

The report recommends adopting a holistic view that builds-in needed biodiversity and resilience. It recognises that wood can be used as a renewable replacement for coal in some instances.  And although wood and wood chips when burnt release carbon dioxide and other air pollution, the carbon is replaced as new trees grow. This may be important, as is discussed below, but the forestry proposals are more sanguine. 

However, the approach to farming and agricultural emissions are misguided in my view. While some progress is readily viable and desirable, to be “first in the world” potentially puts New Zealand farmers at a huge disadvantage relative to others, and in an adverse position in the marketplace until or unless international trade properly deals with tariffs for imports and exports involving carbon. This seems some way off.   

Moreover, there are some notable omissions in the plan, especially with respect to solar, wind and hydro power, and how to deal with intermittency (see below).

With regard to hydroelectric power, New Zealand is already well-placed, but can do more. Wind power is potentially abundant and is developing. Solar power is also available and, although with less potential than in Queensland, prospects are far greater than for Germany, which is streets ahead, especially in rooftop solar, with net metering. 

The issue with wind and solar power is intermittency, and we have been slow to address this (including the Climate Change Commission). Coupling these power sources to hydro, where water is stored behind a dam, would have tremendous potential – but for the fragmented way power companies work in New Zealand.  An integrated national approach is needed, and this is where the Government should play a major role.  

Nowdays, powerful batteries can be used, but a great under-utilised “battery” is pumped hydro.  This is being considered under the NZ Battery Project on Lake Onslow down south, but for the “dry year” problem not for intermittency. Instead, much smaller and more local projects could be used as efficient batteries; many examples exist elsewhere such as in Switzerland and one is being developed in Queensland. In the latter case, at Kidston, an old gold mine is used, and pumped hydro is planned for 250 MW with the height differential between the lower and upper lakes of only 230m.

New Zealand has a role to play as a leader in the South Pacific, as well as at home. But it needs to be embedded in the global context. New Zealand’s emissions contribution is small and wiping it out would not solve the global problem. But we can set an example, and apply pressure to other countries, such as Australia, China, and the United States to get their houses in order. This role is an aspect missing from the plan.

So, what is the global context for climate change?

Major concerns about climate change began growing in the 1980s and led to establishment of  an international treaty,  the United Nations Framework Convention on Climate Change, signed in June 1992. It was understood then that threats to the climate system were not from direct human influences, but rather from  human-induced changes in atmospheric composition that interfered with natural flows of energy through the climate system. 

In particular, the burning of fossil fuels increases carbon dioxide in the atmosphere; carbon dioxide is a greenhouse gas that contributes to global heating by forming a blanket layer over the Earth. As carbon dioxide is long-lived (for centuries,) it builds up in concentrations in the atmosphere, so current values of about 415 ppmv (parts per million by volume) are 48 percent higher than the pre-industrial value of 280 ppmv. Half that increase has occurred since 1985. 

Other greenhouse gases also contribute, notably methane, which is also rising in the atmosphere from human activities, although methane has a lifetime of only a decade or so.  Particulates, often called aerosols, are visible pollution that may block the sun and alter clouds, cause further complications. 

However, it was only in the late 1990s, in part through my own work, that it was understood that global heating had its biggest impacts through changes in extremes of weather and climate. This is because of the key role of water on Earth and the hydrological cycle. Extra heat evaporates surface moisture. This causes drying where it is not raining, adding moisture to the atmosphere that in turn can hold more moisture at a rate of seven percent per degree Celsius, leading to heavier precipitation and risk of flooding. Indeed droughts, heat waves and wildfires at one end of the spectrum, and more intense rains and heavier snows and flooding at the other end, are now widely recognised to be occurring because of climate change.

The Paris Agreement in December 2015 set emissions reduction targets and tracking, and reporting of progress towards meeting those targets to the international community. This includes the goal of “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C”.  The Paris Agreement also commits to enhancing adaptive capacity and resilience to the impacts of climate change. Six years on, most nations are failing to meet their commitments and emissions of greenhouse gases continue without diminution. While many countries have significantly added renewable energy to their mix, demand for energy continues to rise.

A major concern of scientists, not adequately appreciated by the public and politicians, is that evidence of dangers that need policy responses may be delayed or muted by the tremendous inertia in infrastructure and the climate system, so by the time problems are abundantly clear, it may be too late to do anything about it. The longer society delays taking steps to cut emissions of planet-warming greenhouse gases, the more severe and widespread the harm will be. While climate change has always been present, it is estimated current rates of change are more rapid than natural changes by a factor of a hundred or greater. It is the rates of change that are very disruptive, not only to natural ecosystems and biodiversity, but also to society. 

IPCC Reports

A new series of three IPCC reports have recently come out. The first deals with science, the second impacts and adaptation, and the third mitigation: what can be done about it. The first report from November 2021 stated:

“Recent changes in climate are widespread, rapid, and intensifying, and unprecedented in thousands of years.”

It went on to say:

“Unless there are immediate, rapid and large scale reductions in greenhouse gas emissions, limiting warming to 1.5°C will be beyond reach.”

The report itself is written over several years and statements are already out of date. In particular, because it is evident that “rapid large scale reductions in greenhouse gases” are not occurring, the 1.5°C threshold is lost. It is likely to be exceeded by about 2032. Global agreements are not helped by a regional war and global pandemic.

This means that assessing vulnerability and past and expected impacts, and thus planning for expected consequences and adaptation to climate change is essential. But it remains vital to also limit emissions and greatly slow future climate change to allow adaptation to occur and minimise disasters.


Other greenhouse gases contribute to the global problem, notably methane. As methane is a more potent greenhouse gas than CO2, there is a lot to be gained in reducing atmospheric concentrations, and this was recognised at COP26 in late 2021 in Glasgow.  “Over 100 Nations at COP26 Pledge to Cut Global Methane Emissions by 30 Percent in Less Than a Decade” including New Zealand, but not Australia. The potential for reductions is huge in all areas related to “fugitive emissions” that relate to methane vented into the atmosphere, leaks in pipes and abandoned mines, landfills, fracking operations and mining (drilling, extraction and transport) of coal, oil and natural gas. In both Oz and NZ “agriculture”, which includes all cattle, dairy and sheep farming, makes up most methane emissions (70 to 110 Mt/year in Australia and 25 to 28 Mt/y in NZ).  But whereas fugitive emissions are 30 to 37 Mt/y in Australia, they are about 1 Mt/y in NZ.  In other words, the fugitive emissions in Australia exceed all of NZ’s emissions. In the USA fugitive emissions run about 280 Mt/y. Moreover, the scope to reduce those by tracking leaks and eliminating them is huge. 


There has been a lot of hype about growing trees. Indeed, trees take up carbon dioxide through photosynthesis and convert the carbon into the wood and plant material. Trees also have many other desirable attributes and the deforestation in the Amazon and elsewhere in the tropics has been a disaster. Loss of carbon stored in forests and in the ground contributes to increases in atmospheric green-house gases. Reforestation and expanding tree areas (afforestation) have potential to contribute to reduced atmospheric concentrations of carbon dioxide. 

Trees may grow faster with increased carbon dioxide in the air, but other factors, such as drought overwhelm those aspects. Indeed, trees have a finite lifetime and are vulnerable to disease, drought, and wildfire. They depend critically on adequate rainfall and water supply. Several examples exist of trees set aside as “offsets” for carbon emissions that have been wiped out by wildfire. It may be possible to achieve offsets for a specific date, such as 2050, but what happens in subsequent years as the trees saturate and die? Indeed, an old-growth forest, almost by definition, is one that is neutral with regard to carbon dioxide, as the uptake in spring during photosynthesis is offset by the fall of leaves, twigs and dying trees especially in autumn, and forest floor decay. 

A key question is how to harvest mature trees and then grow new ones, and where and how to bury or sequester the old ones forever? The new plan makes some progress by recognising that wood can be used as a renewable replacement for fossil fuels, especially through wood chips, and these may also be exported. While it does put pollution and carbon dioxide into the atmosphere, it is compensated for by the growth of new trees. But it is not then an offset.

In summary, there is a lot to like in the new emissions reduction plan, but more could be done. And, there is insufficient recognition of what the rest of the world is (not) doing.

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