From Heritage New Zealand, Winter 2008

by Rick McGovern-Wilson

Climate change poses a threat to our historic heritage, and, in some cases it may be too late to prevent damage

The earth’s climate has always fluctuated due to natural cycles over many thousands of years, but there is growing concern because the current magnitude of change is unprecedented, and the evidence is increasing that humanity may be directly responsible for the increased rate of change.

The reasons have been widely debated and do not need to be reiterated here. The main change is predicted to be atmospheric warming in the range of 1.1–6.4°C by the end of the century, depending on how we respond to the situation. The Intergovernmental Panel on Climate Change (IPCC) has mapped out six scenarios. In all but one, the best estimate is a rise of more than 2°C on pre-industrial temperatures, but in three it is possible that the increase will be more than 4°C. The most noticeable outcome will be a sea-level rise of 0.2–0.85 metres by the end of the century.

This is the result of thermal expansion of the oceans combined with glacial melt. If the polar ice-sheets also begin melting, the rise could be up to five metres in places. Already we are seeing the retreat of Arctic ice during the northern summer, and the Wilkins Ice Shelf on the Antarctic Peninsula spectacularly began cracking in March. The increase in sea level, coupled with increased storm events and tidal surges, will have devastating effects on low-lying coastal zones, let alone islands of the Pacific and Indian Oceans. In many places, other changes are already visible: Venice struggles with increased sea levels; many countries across Europe face drought, floods and storms as global temperatures rise; and, in the Sub-Sahara, desertification is becoming a huge problem.

The primary causes of these increases are greenhouse gas emissions, in particular carbon dioxide, methane and water vapour. All act as an impervious layer that traps the incoming heat from the sun, thus leading to a progressive warming of the earth’s surface. In response to the threat, the Kyoto Protocol, signed in 1997, set targets for developed nations to slash their greenhouse gas emissions by 2012.

If lowland parts of Asia and Europe, along with the Pacific Islands, are inundated, there is high potential for increased migration. University of Queensland archaeologist Dr Marshall Weisler has studied the effects of rising sea levels on islands of the central Pacific and Indian Oceans. He predicts that whole nations may have to be abandoned within a generation if the sea continues to rise at the current rate.

So far, little attention has been focused on the risks to the world’s cultural and historic heritage. International co-operation to develop methods of adaptation and mitigation is urgently needed but, to date, the potential impact on cultural heritage has been little recognised. The 2007 IPCC report, the key information document for policy makers worldwide, contains no reference at all to the historic environment.

The seriousness of the issue cannot be under-estimated. At the International Council on Monuments and Sites conference in Cairns last year, John Hurd, director of conservation for the Global Heritage Fund, presented stark evidence of the effects on a range of historic heritage sites in the Himalayas, on the steppes in Central Asia and in sub-Saharan Africa. The conference was based around the theme, “eXtreme [sic] heritage: managing heritage in the face of climatic extremes, natural disasters and military conflicts in tropical, desert, polar and off-world landscapes”.

Hurd works in central Asian deserts (Kazakh, Tibet tablelands, China, Russia) where populations in the hundreds of thousands are having to shift because of global climate change. In the desert, they used to get gentle rain for two months in the spring; it is now raining irregularly in violent storms in northern Afghanistan (an area known as the “Desert of Death”, which is a salt desert). This type of rainfall tends to mobilise salts in the ground and bring them to the surface, where they are distributed by the wind, and poison wells.

Hurd is working on 17 sites worldwide, and is getting site managers to collect climate data. The 256-square-kilometre Otrar Oasis in Kazakhstan, on the cross-roads of the east-west Silk Road and the north-south migration route for steppe herders, is the site of seven mounds (tobe) that indicate where the oasis towns were built up. Otrar Tobe, the largest, was founded around 200BC, and flattened by Genghis Khan. One tobe was excavated by the Soviets 70 years ago, but they left the excavations exposed, and extreme rainfall has caused the mud brick walls of the city to “melt”.

Other mechanisms of decay include tourists (who ride their horses on the walls and have parties in the site) and rising salts. As part of its conservation work, the Global Heritage Fund establishes field labs and does empirical testing. Once the environmental regime for that site is understood, repair and maintenance work can proceed.

At Otrar, there were seven square kilometres of exposed archaeological material to preserve and, therefore, there was a need to prioritise – 95 per cent had to be condemned. Of the 5 per cent chosen to be conserved, 95 per cent was backfilled, and the rest was conserved. Over winter, some areas have structures built over them for protection.

At the Basgo Monastery and fortress in the Trans Himalaya, Hurd and his team use earth “staples” to stabilise large cracks in the earth walls.

In the Arctic, the decrease in sea ice and increase in storm surges are severely eroding Inuit sites and the remains of Royal Canadian Mounted Police mission sites and forts. The adaptive response is to undertake salvage excavations.

The UNESCO World Heritage Committee has endeavoured to take a lead in protecting cultural heritage sites. A survey of member states found 46 World Heritage Sites considered to be already affected by climate change in the form of storms, sea-level rise, drought, increased rainfall, desertification and temperature increase.

The committee adopted policies at the 2006 (Vilnius) and 2007 (Christchurch) meetings to guide the way the international community will address the problem for sites that are already on the World Heritage List and ones that are being nominated. Importantly, the decisions taken by the committee recognise the need to carry out scientific research to provide firm evidence of the effects of climate change, to ensure that the impact on both cultural and natural heritage is taken seriously in the future.

English Heritage, likewise, is taking a key leading role at a national level, initiating projects to establish data for the future management of buildings and landscapes. Mary Cassar’s 2005 report acts as a guide for much of the subsequent work. A new view of conservation is slowly developing – many professionals in the heritage industry have been brought up with the understanding that conservation typically means preservation. It is now seen that conservation is about understanding and managing change.

Across the Tasman, the impacts are likely to include an increase in annual average temperatures, which will be significant in some areas; more heat waves, fewer frosts; more El Nino events; possible decreases in rainfall; more storm surges along the coast; increase in severe weather events; change in ocean currents; and sea-level rises as predicted for the rest of the globe.

Australia has been occupied for 40,000-60,000 years, and the prehistoric sites contain a record of constant change. The difference now is that we can make pro-active responses.

The effects of global climate change in New Zealand will be variable. The NIWA summary of the 2007 IPCC report as it pertains to New Zealand states: “Heat waves and fire risk are virtually certain to increase in intensity and frequency. Floods, landslides, droughts and storm surges are very likely to become more frequent and intense, and snow and frost are likely to become less frequent.”

The eastern regions will be most at risk from drought. NIWA predicts a 0.3-metre rise in sea levels by 2050, and 0.66 metres by 2080, but it could be as high as 0.8 metres, which, combined with a storm surge and high tides, would spell trouble for low-lying coastal areas.

The Kyoto Protocol required New Zealand to reach a 5.2 per cent reduction in 1990 emissions levels by 2012. To date, we are 24.9 per cent up on 1990. The United Nation’s Bali conference on climate change last december recommended a reviewed target of 25-40 per cent for developed countries.

The government is debating the Climate Change (Emissions Trading and Renewable Preference) Bill as a formal process to reduce greenhouse gas emissions by reducing net emissions and complying with international obligations, “while maintaining economic flexibility, equity and environmental integrity at least cost in the long-term”.

So, although it is likely we will endure changing weather patterns, changing distribution of plants and animals and increased sea levels, there has been no planning for the protection and management of our heritage.

Based on the English Heritage experience, the primary threats to built heritage are flooding, rainwater penetration, subsidence and the spread of pests and diseases due to changing weather patterns. Practical solutions, such as larger capacity guttering and downpipe systems to cope with heavier rainfall, may detract from the buildings but, in the long-term, they will protect them.

Built heritage will survive extreme climate events if well maintained. A unique aspect of New Zealand’s heritage landscape is Maori built heritage. Many of these buildings, especially on marae, are wooden, and make a lot of use of natural fibres, such as flax, and natural colourants. Many do not contain adequate mechanisms for reducing moisture levels, such as heat pumps, dehumidifiers and air conditioning, and fire risk is always problematic. Extreme weather changes are going to be just as deleterious on these structures, and they deserve a special focus of attention.

Many direct threats to coastal sites are part of long-term natural processes that occur over hundreds, if not thousands, of years but the rate of change will increase markedly. In 2007, Kerikeri experienced in six months three 1-in-300-year flood events that came very close to the Stone Store and graphically illustrated the potential threat to our heritage icons.

But, if things are as bad as the scientists claim, what else could we expect in future?

• Inundation of coastal sites will destroy a large amount of our archaeological heritage, especially that of the early Maori settlement.
• Most of the 6000 recorded pa sites are on hills and ridgelines, and more storms will lead to increased erosion and potential loss of sites.
• Events like Cyclone Bola in 1987 will become more frequent and cause greater damage.
• Increased damp and higher water levels, resulting in rising salts in stonework and masonry.
• Increased rot in wooden buildings.

It is a long-term issue, but we must plan now because it will take a long time to prepare and respond. Government climate-change policy is targeted at environmental impacts but not those that will affect cultural heritage.

The New Zealand Historic Places Trust, as the Crown’s lead heritage agency, must take a lead not only in developing the required policy but also in the way it manages its buildings portfolio on behalf of the people of New Zealand. We can make deliberate protective decisions for cultural heritage.

We need to undertake coastal surveys and monitoring to establish the state of the archaeological resource. Many of these will need to be multi-party studies that can bring a range of interests to a site. This can complement work that has already been initiated in Southland and the Coromandel.

In the latter, a project by NZHPT and private consultants has already conducted three one-week surveys along the east coast, focusing on the state of sites, and making recommendations for their future management (see sidebar).

Along the Foveaux Strait coast of Southland, a major project undertaken by Department of Conservation, Environment Southland, the NZHPT, Kaitiaki Runaka o Murihiku, New Zealand Archaeological Association and Southern Pacific Archaeological Research recorded baseline data on site distribution and condition, and established monitoring points for future resurvey.

These coastal surveys need to provide an improved knowledge of the nature, conditions and threats acting upon the archaeological and historical sites along the coastlines, identify sites of high value for protection, identify sites under great or extreme threat requiring pro-active remedial work or excavation, and to record baseline data for ongoing monitoring.

We also need to complete significance statements to determine which of our coastal archaeological sites must be saved at all costs, which cannot be saved but must be excavated to recover information before it is lost, and which we can afford to lose. Given that all the Polynesian first-contact sites are to be found on the coastal margin, this is a highly significant issue, and will require detailed input from tangata whenua.

The most important mind-shift that we must develop is that we cannot save all the sites, and we cannot afford to excavate all those that we cannot save. There will be a vast majority for which we will have to accept there is nothing that can be done, and we will simply have to lose them.

There is potential for archaeological research strategy development to study impacts over time with changes to site structure and relationship to the environment. Part of the response, via salvage excavations, given the resources required (digging it up, storing the material, conserving it, studying/reporting), may reach the stage of saying “is it worth it?”

We need to identify those stone and wooden buildings that may require remedial and protection works. NZHPT buildings must be prepared and the NZHPT must show leadership for individuals.

From these actions, there are a range of management options we can promote. They include better modelling at a local level for territorial local authorities; better monitoring of ongoing effects on cultural sites; better exchange of information between public jurisdictions and the private sector, and within the community; the development of guidelines and case studies looking at adaptation responses and processes; development of disaster mitigation plans as part of management planning; initiation of site recording programmes to identify sites at major risk, giving priority to excavating those where necessary; and funding of exemplar projects that demonstrate preparedness