Past climate variations over New Zealand

NIWA's evaluation of New Zealand's past climate has recently been criticised.

Our response to these criticisms

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Methods of inferring past climate

Instrumental Measurements and written or oral records provide quantitative records of temperature and other meteorological records for the past 150 years in New Zealand. Such records must be analysed carefully, to identify the influence of any non-climate factors (such as changes in observing site or method, or encroaching urban development). Scientists from NIWA, Otago and Auckland University have put substantial effort into examining, correcting and analysing temperature and other meteorological variables from New Zealand and South Pacific islands. Records of sea level and of land movements are important for assessing sea level change.

Proxy data

Beyond the scope of the instrumental measurements, information about past climate can be obtained from natural proxy archives.  Changes observed in these archives often identify so closely to climate variations that they can be used as a substitute for climate records prior to the instrumental record after a careful calibration process has been undertaken. Piecing evidence together from various proxy data sources, includes:

Ice cores: Ice cores drilled in Greenland, the Antarctic ice sheets, the Himalaya, and in other alpine regions of the World comprise very important archives because they provide extensive detailed information about past climate variability and atmospheric composition. The ratio of oxygen isotopes in ice can indicate the temperature at the time ice was deposited as snow. Air bubbles can be analysed to measure atmospheric carbon dioxide and methane concentrations at the time the bubbles were trapped in the ice. Dust trapped in the ice may indicate windy, arid conditions.  Geochemistry, including trace elements and salts, can tell a story about regional atmospheric circulation. The core from the Russian Vostok station in Antarctica provides information back to at least 160,000 years ago, and when drilling is completed a climate record of the past 500,000 years is probable. More details are given on the Australian Antarctic Division website.

Australian Antarctic Division 

Fossil Pollen and Phytoliths: Different classes of plants produce pollen grains and phytoliths (siliceous formations precipitated by plants) that have distinctive shapes. Pollen grains and phytoliths are often found preserved in sediment cores from ponds, lakes and marine environments. They provide information about the plant communities that grew nearby when the sediments were deposited, yielding detailed information about ecological and climatic conditions that prevailed at particular times in the past. Many pollen and phytolith records are dated using radiocarbon and also by association with well-dated volcanic ash fall deposits known as tephra.

Lake sediments: Composition and sedimentation rates in lakes change in response to variations in environmental conditions during periods of wet and dry climate. Pollen in the sediments can indicate the type of vegetation present, and plankton biota indicates physical and chemical conditions in the lake water.  In some cases, stark seasonal changes in lake inflows and sedimentation can cause annual layers to form in lake sediments.  Annual layers, or varves, commonly form in lakes fed by glacial meltwater, and can be used to infer the amount of melted ice and what past warm season temperatures were like.  Within the sediment layers, microfossils like diatoms, bugs, and plant material are preserved.  These fossils can also reveal information about what past environmental conditions were like, sometimes with incredible precision.

Ocean sediment cores contain primitive shelled animals (foraminifera) whose abundance in the surface layers of the ocean depends on surface water temperature and other conditions. Off New Zealand the rate and type of sediment deposition depends on factors such as the amount of glacial activity and on other climate-driven erosion processes. Pollen types and the isotopic composition of material in the sediments provide further information on past climate. Cores obtained off New Zealand from the international deep sea drilling project provide information as far back as 6.3 million years, and drilling of more cores is planned. New Zealand is coordinating an interesting international drilling project near Cape Roberts in Antarctica, to establish more information about past Antarctic climate and ice extent.

Loess are fine-grained wind-blown dust deposits on land. They typically accumulate during periods characterised by dry and windy conditions.  In New Zealand, they are associated with cool and cold intervals that coincide with glacial advances. Numerous loess sections can be found on the South Island, particularly in eastern regions.

Glaciers: Variations in the past size of glaciers can be inferred from the location of moraines (rocks and debris deposited by glaciers that mark a former ice margin position), outwash fans, buried soils, and by the presence of glacial features in the landscape. In New Zealand, cool summer temperatures are only one factor in promoting ice accumulation on glaciers, and snow accumulation rates also respond to changes in the strength and direction of the westerly wind flow and sea level pressure in summer. More details are given in a paper by Blair Fitzharris and his colleagues (Fitzharris et al., 1992).

Speleothems are used to describe a stalactite, stalagmite or flowstone cave deposit of crystalline nature.  These deposits occur within karst terranes in subterranean caverns mainly as calcite (CaCO3) precipitated from groundwater that percolated through overlying limestone or marble rock.  Interior cave climates and environments are generally stable; temperatures have little annual variation and are usually close to the external local mean annual air temperature.  Oxygen and carbon stable isotope values (18O/16O and 13C/12C) obtained from speleothem calcite have been employed at many locations in the world to determine past climate conditions and can be used to interpret environmental changes. Professor Paul Williams at the University of Auckland has devoted much of his career to speleothem research. His work has shown the relationship of δ18O signal in speleothems contains a strong temperature component while periodic changes in the water balance are suggested to be a likely cause of variations that occur in the δ13C signal.  Speleothem records from New Zealand extend back more than 200,000 years, and have been used to indicate periods of glacial advance.  Speleothems can be dated using uranium-thorium isotope techniques and usefully provide detailed information across many different time periods with varying resolution. Most recently, paired records in eastern North Island and western South island were used to show changing climate regimes for New Zealand during the Holocene (Lorrey et al., 2008).

Tree rings are some of the best resolved records of past climate in the world. This is because, in many cases, one tree ring is grown per year, allowing tree rings to be dated with great precision and with annual resolution. Tree growth is dependent on many factors. However, common growth patterns often emerge at the regional scale between trees, suggesting there is a common growth response to climate changes. Correlations of tree ring data with soil moisture, temperature, and precipitation often enable tree ring records to be substituted for instrumental climate data into the distant past.  In the case of New Zealand, which has many long lived tree species suitable for dendrochronology, long climate reconstructions of droughts, storms, and even El Niño events are possible.  Tree ring climate research is very active in New Zealand, and researchers affiliated with the University of Auckland Tree Ring Lab in the School of Geography, Geology, and Environmental Science are presently undertaking palaeoclimatology studies. Tree rings can also be used to accurately date minimum ages of glacial advances and retreats during the last millennium.  There are many current climate change collaborations in New Zealand that NIWA climate scientists contribute to within the tree ring research field.

University of Auckland Tree Ring Lab 

Boreholes: It is sometimes possible to deduce past surface temperatures going back several hundred years by measuring the way temperature varies with depth in a borehole several hundred metres deep (at a suitable site not disturbed by groundwater flow). This is because fluctuations in ground surface temperatures propagate slowly downwards into the earth as a "temperature wave".

Climate variations during the past 150,000 years

The figure below shows past air temperatures, carbon dioxide concentrations, and methane concentrations inferred from the ice core from the Russian Vostok station on the Antarctic icecap. This figure is often taken (e.g. in various IPCC Scientific Assessment reports) as a general indicator of global variations over the past 150 thousand years.

IPCC Assessment reports 

 

Figure 1: Dust concentration, climatic air temperature, and concentration of carbon dioxide and methane from measurements of trapped air in the Vostok ice core, plotted against time before present. (from the Australian Antarctic Division web site, Hobart, Australia. The original sources of the information are Petit et al (1990) and Lorius et al (1993)).

 

Australian Antarctic Division 

New Zealand temperatures over the past 150,000 years appear to broadly reflect those seen in the Vostok record displayed above, although there are some important differences on multimillennial and finer time scales. Palaeoclimate information indicates that the Oturi interglacial (the last interglacial before our current interglacial period) includes three identifiable periods of milder climate 140,000 to 120,000, 100,000 and 80,000 years ago respectively (Pillans, 1983), with temperatures at the end of the Oturi 1 to 2°C below present day values (Salinger and McGlone, 1990). (An "interglacial" indicates a relatively warm period when glaciers and ice caps have retreated, while a glacial is a period of extensive ice cover). Climatic cooling marked the beginning of the Otiran glacial stage at about 70,000 B.P. Glaciations are marked by expanded New Zealand mountain glaciers over the period 70,000 to 15,000 years ago, although there is evidence of an important moderation of climate between 60,000 to 30,000 years ago. The Last Glacial Maximum was between 26,000 and 18,000 years ago, with New Zealand temperatures estimated to be 4 to 5°C below present day values. At this time palaeovegetation patterns indicated enhanced westerly circulation over New Zealand.  At present, a consortium of New Zealand and international researchers comprise the NZ-INTIMATE (INTegrating Ice core, Marine, and Terrestrial records) group, which is using multi-proxy data to outline the structure of the last ice age for New Zealand.  Key aims of the group are to determine the key components and timing of New Zealand glacial history, and how it compares to other records from the Northern and Southern Hemisphere. 

More information at the New Zealand Paleoclimate Research website 

 

Figure 2: New Zealand’s estimated mean yearly temperatures since the last ice age. From Fig 5.6 of Ministry for the Environment (1997), based on Salinger (1988). This plot does not show the temperature rise of around 0.7°C that occurred over the 20th Century, because of the very compressed horizontal scale.

 

During the Holocene (the current interglacial period which began about 10,000 years ago here), average annual temperatures for New Zealand appear to have fluctuated between about 10 °C and 14°C (Salinger 1988). The beginning of the Late Glacial (14,000 – 10,000 B.P.) was heralded by rapid warming, with glacier retreat and ice diminishing to volumes close to that of present-day amounts by 12,000 B.P. There was a brief cooling at around 11,500 B.P. The warmest conditions of the present cycle occurred between 10,000 and 6,000 B.P with temperatures about 1°C above modern values. This warmer climate was mild, with light winds and lush forests. Moisture changes derived from past vegetation patterns indicate stronger north to north west airflow over New Zealand. Speleothems indicate a lowering of temperature after 7,000 B.P, with a resurgence of small glacial events in the Southern Alps at 5,000 B.P. with strengthening westerly wind flow. By 2,500 B.P. New Zealand’s modern climate and broad scale circulation patterns were probably established, with more frequent and stronger west to south west flow (Salinger and McGlone, 1990). Glacial advances in southwestern New Zealand and natural forest fires in eastern South Island began to occur, indicating that zonal flow had strengthened, and that the east was periodically subject to extreme temperatures and dryness. These variations may have been partly due to establishment of modern El Niño Southern Oscillation behaviour, which continues to exert a strong impact on New Zealand’s weather and regional climate characteristics. The average temperature over New Zealand in the 3,000 years leading up to the early 20th century is thought to have remained within about 1°C of 12°C, which is about 3°C below the global average. 

More information about the El Niño-Southern Oscillation

The period from 850 to 1850 AD was one of variable climate for New Zealand. From South Island mountain glacier records, cooler periods of climate occurred in the 11th century, early 12th century, mid 13th century, early 15th century, early 16th century 17th and 18th centuries and the mid 19th century. Tree ring evidence (Salinger et al., 1994) shows cooler November – March periods in the 1760s, around 1790 and the early 1840s to early 1860s. These times correspond to periods when the glaciers had advanced (Fitzharris et al., 1992).  Similarities between the New Zealand climate changes during the last millennium using tree rings (Cook et al., 2002) has been compared to the Northern Hemisphere Medieval Warm Period and Little Ice Age (Lamb, 1965). However more work is needed to define these climatic intervals more clearly in the New Zealand region, and to determine how similar the changes were to those observed in the Northern Hemisphere.

Climate variations over the last 140 years

Surface temperature trends for New Zealand and parts of the South West Pacific can be reconstructed from land and marine surface temperature observations made since 1860. More complete climate data exists for much of the region since the 1940s. Salinger et al (1995) have homogenised and analysed trends in South Pacific island temperature and rainfall. Surface marine data have been taken from an updated version of the Global Sea Ice and Sea Surface Temperature (GISST) marine data set (Rayner et al., 1995). All these records have been homogenised to remove any artificial trends as far as possible (Folland et al., 1997).

Temperature, Clouds and Diurnal Temperature Range.

The South Pacific can be split into the four regions shown below, each of which displays somewhat different behaviour in temperature trends (Salinger et al., 1995). These are the Central Pacific (T2) and Convergence Zone (T4) regions which lie on or east of the Intertropical Convergence Zone and the South Pacific Convergence Zone (SPCZ), and the South-East Trades (T1) and New Zealand regions (T3) which lie to the south of these circulation features. Longer term trends are only available in the annual temperature time series for regions T1 and T3.

 

Figure 3: The four zones of coherent temperature behaviour in the South Pacific, from Salinger (1995)

 

In the New Zealand region (T3) the magnitude of warming between the decades 1861 – 70 and 1981 – 90 is 1.1°C. Temperatures increased sharply after the 1940s, but annual mean warming has slowed recently. There is generally very good agreement for the region on all time-scales between quality controlled sea surface temperature (SST) and air temperature measured at night over the surrounding ocean surface (NMAT), and mean air temperatures averaged over New Zealand. The SST increase between 1900 and 1980 is 0.8°C. These temperature trends agree with recent behaviour of the South Island mountain glaciers, from modelling studies (Ruddell, 1996). Most glaciers were at their furthermost extent when first surveyed in the 1860s. With improvement in glacier dynamics, steady state analysis of a wide variety of glaciers shows that recession since the late 1800s is because of a temperature increase of 1.0 ± 0.3°C. 35 percent of the mass of the glacier ice has been lost since this time, amounting to 35 km3 of water. Boreholes (Whiteford, 1996) also confirm the warming trend.

 

Figure 4: Annual mean temperatures in the T3 (New Zealand) Region from Salinger (1995), expressed as differences from the1951 – 1980 average. The curved line indicates variations at decadal and longer time scales.

 

In the South East Trades region (T1) mean temperatures trend steadily upwards from 1910. The temperature increase between decades 1911 – 20 and 1981 – 90 amounts to 0.8°C, with the first decade being the coolest, and the last the warmest. Good agreement occurs with SST and NMAT records, the former showing a warming of 0.7°C.

 

Figure 5: Annual mean temperatures in the T1(SouthEast Trades) Region from Salinger (1995), expressed as differences from the1951 – 1980 average. The curved line indicates variations at decadal and longer time scales.

 

In the South East Trades region (T1) mean air temperature increases are found to be due to warming of both maximum and minimum air temperatures, with little change in diurnal temperature range (Salinger, 1995). At the same time sunshine shows a small, but clear increase, while there is little trend in 0900 cloud cover (Table 1). Trends in the Central Pacific (T2) show a decrease in island temperature of about 0.2°C from the late 1930s to around 1965, followed by a sharp increase of about 0.8°C. Trends in SST are similar. Minimum air temperatures have increased by almost twice as much as maximum air temperatures, with a significant decrease in DTR in the Central Pacific (T2). This relates closely to significant decreases in sunshine (-1.7%/decade) and increases in cloud cover.

 

Region Mean temp Max temp Min temp DTR Sunshine total 0900 cloud amount

SE Trades (T1)

0.11

0.11

0.12

-0.01

0.7

0.00

Central Pacific (T2)

0.14

0.10

0.19*

-0.08*

-1.7*

0.09

New Zealand (T3)

0.12

0.08

0.15

-0.07

-0.6

-0.07*

ITCZ and SPCZ (T4)

-0.01

0.01

-0.02

0.04


-0.20*

New Zealand Subregions

Western NI

0.13

0.07

0.18

-0.11

0.2

-0.10*

Eastern NI

0.16

0.14

0.18

-0.04

0.1

-0.04

Western SI

0.18

0.11

0.07

0.03

-1.6

-0.01

Eastern SI

0.10

0.07

0.12

-0.06

0.0

-0.03

Inland Central

0.11

0.04

0.19

-0.15*

0.4

0.04

Southland

0.14*

0.06

0.22*

-0.16*

-1.9*

0.01

Table 1. Trends in annual mean, maximum and minimum air temperature, Diurnal Temperature Range (°C/decade), sunshine (%/decade) and 0900 cloud amount (oktas/decade) for the south west Pacific and New Zealand for the period 1951 - 1990. Asterisks indicate significance at the 95% confidence level.

 

Mean air temperatures have increased by 0.12°C/decade in the New Zealand region (T3). Minima have increased at almost twice the rate of maxima (0.15 cf 0.08°C/decade), with a consequent decrease in diurnal temperature range (DTR). Sunshine has also decreased (-0.6%/decade), as has cloud cover. In New Zealand cloud cover is modified by the country’s rugged orography. Region T4 is the only sub-region of the South Pacific not to display increases in mean air temperature. However, DTR in this region increases, and cloud cover decreases significantly.

In New Zealand, the responses of maximum and minimum air temperature, DTR, sunshine and cloud amount are all dominated by the interaction of regional circulation with the hills and mountains. Westerly circulation has increased in the New Zealand region over the last four decades. Three of the four regions exposed to this westerly circulation show DTR decreases (Table 1), but only one (Southland) shows a significant decrease in sunshine.

Precipitation

Precipitation has increased in the south west Pacific to the north east of the SPCZ, whilst precipitation decreases have occurred near and south west of the SPCZ. For New Zealand, distinct region changes in precipitation occur since 1930 (Salinger and Mullan, 1996). Summer rainfall was higher in North Canterbury, and lower in the north and west of the South Island from 1930 – 50. The period 1951 – 75, when increased east and north east airflow occurred over New Zealand, showed increased rainfall in the north of the North Island, particularly in autumn, with rainfall decreases in the south east of the South Island, especially in summer. The 1976 - 94 period is notable for several strong El Nino events. Significant annual rainfall trends have occurred with rainfall decreases in the north of the North Island, and increases in much of the South Island, except the east. Rainfall has increased in winter in all parts of New Zealand except the south east of the South Island.

One of the important consequences expected in a warming climate is an increase in extreme rainfalls. This occurs because of higher potential moisture content in air at higher temperatures, and a shift towards more convective rainfall in the models. Observations have shown an increase during the 20th century in extreme rainfalls in many parts of the world (IPCC, 2007a, Fig TS-11a in Technical Summary). However, a recent analysis of New Zealand daily rainfall does not show a uniform trend over the country due to the interaction of atmospheric circulation and the country’s complex topography. Griffiths (2005) has analysed a number of indices of extreme daily rainfall, for the periods 1930-2004 and 1950-2004. Western sites tend to show a significant increase in daily rainfall extremes, but eastern sites a decrease. Figure 6 shows an example of trends in the number of days per year with rainfall exceeding 25 mm. Nevertheless, NIWA recommends in the guidance manual (MfE, 2008) that increasing future rainfall extremes should be assumed everywhere (see next section), until such time as more research can identify any regional differences.

 

Figure 6: Trends in number of days with rainfall above 25 mm from 1950-2004.

 

Interannual Variability

In New Zealand and the South Pacific, the El Niño Southern Oscillation (ENSO) is a significant source of seasonal and year-to-year climate variability (Nicholls, 1992). Opposite interannual air temperature from detrended time series occur on either side of the South Pacific Convergence Zone (SPCZ). The Southern Oscillation Index (SOI) explains up to 40% of year-to-year air temperature variations in these areas. When the Southern Oscillation Index (SOI) is positive, mean annual air temperature anomalies are positive in the area south west of the SPCZ (T1 and T3), and negative to the north east of the SPCZ (T2 and T4). (Salinger et al, 1996). Opposite air temperature anomalies occur during the El Niño phase (SOI negative).

More information about the El Niño-Southern Oscillation and the SOI

Similarly, mean annual precipitation anomalies (Hay et al, 1993) show marked interannual variability, and are also closely associated with the ENSO cycle (Figure 3.4). The SOI also explains over 40% of year-to-year variations in precipitation to the south west and north east of the SPCZ. Near and south west of the SPCZ, above average precipitation occurs when the SOI is positive (La Niña phase), and further to the north east precipitation is below average. Opposite anomalies characterise the El Niño phase.

Decadal Variability

NIWA scientists have recently identified a long-lasting "shift" in New Zealand’s climate that occurred around 1977 (Salinger and Mullan, 1999). The shift was characterised by more persistent westerlies on to central New Zealand since 1977, resulting in the west and south of the South Island being about 10% wetter and 5 % cloudier with more damaging floods. The north and east of the North Island have on average been 10% drier and 5% sunnier, compared to 1951-76 data. This changepoint of 1977 coincided with an eastward movement in the longitude of the South Pacific Convergence Zone, and more frequent El Nino events in the recent record.

This shift is probably due mainly to a Pacific-wide natural fluctuation that in the USA is called the Pacific Decadal Oscillation (PDO, Mantua et al., 1997), which exhibits phase reversals about once every 20-30 years. The influence of the PDO is well-known in the North Pacific, and has recently also been noted in Australian rainfall ( Power et al., 1998), and in the South Pacific Salinger et al., 2001; Folland et al., 2002). Scientists from Pacific Island countries attending a workshop in Auckland in November 2001 put out a press release suggesting the PDO underwent another phase reversal in 1998. Note that in New Zealand, Australia and U.K. this oscillation is referred to as the Interdecadal Pacific Oscillation (IPO).

Long-term warming trends are superimposed on these decadal climate variations. Individual El Nino events bring cooler conditions to New Zealand (see our El Niño page linked to below). However, since 1977 temperatures have continued to rise, resulting in warmer night time temperatures and fewer frosts nationwide, and a increase in very hot days in eastern areas in recent decades.

More information about the El Niño-Southern Oscillation and the SOI

Ocean Temperatures and Sea Level

Repeat measurements of temperature and salinity from the surface to the bottom of the ocean were carried out for a section across the Tasman Sea at 43 °S, in March 1967, and September 1989 / March 1990. Below 300m, where seasonal effects can be ignored, two regions of coherent warming spanning the full width of the Tasman Sea were observed (Bindoff and Church, 1992). These regions were centred at depths of 700 m (5 – 10 °C water) and 3,000 m (1.3 – 1.9 °C water).

New Zealand has four tide gauges with records for 75 years or longer (Auckland, Wellington, Lyttelton and Dunedin). Hannah (1990) used these data to calculate a rising trend in sea level of 1.3, 1.7, 2.3 and 1.4 mm per year respectively, giving New Zealand a mean of 1.7 mm per year. An update by Hannah (2004) confirmed that sea levels around New Zealand have been rising at an average rate of 1.6mm/year over the last 100 years.

Note also that the El Niño Southern Oscillation (ENSO) is a significant source of seasonal and year-to-year variability in sea level. For example at Moturiki (Mt Maunganui), the seasonal and interannual variability account for about 30% and 25% respectively of the variation in non-tidal sea level (Bell and Goring, 1998). On the same NE coast during El Niño events, seasonal sea levels can be depressed by up to 10 cm (accompanied by a fall in shelf sea surface temperatures) while during La Niña phases, sea levels can be elevated by up to 8 cm (Bell and Goring, 1997).

New Zealand annual temperature series updated to 2010

The previous section describes an analysis of temperature trends and variability published in 1995, which used a data set extending only up to 1990. For completeness, we have also included Figure 7 (below) to show the annual New Zealand temperatures right up to the end of 2010. Points of interest since 1990 include the cool period in 1992-93 associated with the injection of small particles high into the atmosphere by the eruption of Mount Pinatubo, and the high temperature in 1998 (the warmest year for New Zealand since measurements began). The 1998 warming was apparent in the Tasman Sea to considerable depth (Sutton et al., 2005; Bowen et al., 2006) and happened to coincide with the end of an El Niño event when New Zealand temperatures are usually below normal.

 

Figure 7:  Mean annual temperature for New Zealand, calculated from NIWA's 'seven-station' series. This series uses climate data from seven geographically representative locations. The data are adjusted to take account of factors such as different measurement sites. The blue and red bars show the difference from the 1971-2000 average. The black dotted line is the linear trend over 1910 to 2010 (0.96°C/100 years).

 

Some useful references

Bell, R.G.; Goring, D.G. (1997). Low frequency sea level variations on the northeast coast, New Zealand. In: Pacific Coasts and Ports ’97, Proceedings of the 13th Australasian Coastal and Ocean Engineering Conference, Christchurch, New Zealand, Vol. 2, pp. 1031–1035. Centre for Advanced Engineering, University of Canterbury, Christchurch.

Bell, R.G.; Goring, D.G. (1998). Seasonal variability of sea level and sea-surface temperature on the north-east coast of New Zealand. Estuarine, Coastal and Shelf Science 46(2): 307–318.

Bhaskaran, B.; Renwick, J.; Mullan, A.B. (2002). On the application of the Unified Model to produce finer scale climate information for New Zealand. Weather and Climate 22: 19-27.

Bindoff, N.L.; Church, J.A. (1992). Warming of the water column in the south-west Pacific. Nature 357: 59–62.

Bowen, M.M.; Sutton, P.J.H.; Roemmich, D. (2006). Wind-driven and steric fluctuations of sea surface height in the southwest Pacific. Geophysical Research Letters 33: doi 10:1029/2006GL026160.

Cook, E. R.; et al. (2002). Evidence for a 'Medieval Warm Period' in a 1,100 year tree-ring
reconstruction of past austral summer temperatures in NZ. Geo.Research Letters 29: 1667.

Fitzharris, B.B.; Hay, J.E.; Jones, P.D. (1992). Behaviour of New Zealand glaciers and atmospheric circulation changes over the past 130 years. Holocene 2: 97–106.

Folland, C.; Salinger, M.J.; Rayner, N. (1997). A comparison of annual South Pacific island and ocean surface temperatures. Weather and Climate 17: 23–41.

Folland, C.K.; Renwick. J.A.; Salinger, M.J.; Mullan, A.B. (2002). Relative influences of the Interdecadal Pacific Oscillation and ENSO on the South Pacific Convergence Zone. Geophysical Research Letters 29: doi: 10.1029/2001GL014201.

Griffiths, G.M. (2005). Changes in New Zealand daily rainfall extremes 1930-2004. Weather and Climate 26: 30–46.

Hannah, J. (1990). Analysis of mean sea level data from New Zealand for the period 1899–1988. Journal of Geophysical Research 95(B8): 12399–12405.

Hannah, J. (2004). An updated analysis of long-term sea level change in New Zealand. Geophysical Research Letters 31: doi 10:1029/2003GL019166.

Hay. J.E.; Salinger,M.J.; Fitzharris, B.; Basher, R. (1993). Climatological seesaws in the Southwest Pacific. Weather and Climate 13: 9–21.

Lamb, H.H. (1965). The early medieval warm epoch and its sequel. Palaeo-3. 1: 13-37.

Lorius, C.; Jouzel, J.; Raynaud, D. (1993). The ice core record: past archive of the climate and signpost to the future. In: Antarctica and environmental change, pp. 27–34. Oxford Science Publications.

Lorrey, A.M.; et al. (2008). Speleothem stable isotope records interpreted within a multi-proxy
framework and implications for N. Zealand palaeoclimate reconstruction. Quat. Int’l. In press.

Mantua, N.J.; Hare, S.R.; Zhang, Y.; Wallace, J.M.; Francis, R.C. (1997). A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin of the Amererican Meteorological Society 78: 1069–1079.

Ministry for the Environment (1997). The State of New Zealand’s Environment 1997. Ministry for the Environment, Wellington.

McGlone, M.; Hope, G.; Chapell, J.; Barrett, P. (1996). Past climate changes in Oceania and Antarctica. In: Bouma, W.J.; Pearman, G.I.; Manning, M.R. (eds). Greenhouse – Coping with Climate Change, pp. 81–99. CSIRO Publishing, Collingwood.

Neil, H.L.; Nelson, C.S. (1994). Oceanic evidence for past New Zealand climates. In: Paleoclimates and climate modelling, pp. 20–24. Misc. Series 29. Royal Society of New Zealand, Wellington.

Nicholls, N. (1992). Historical El Niño/Southern Oscillation variability in the Australasian region. In: Diaz, H.F.; Markgraf, V. (eds). El Niño: Historical and paleoclimatic aspects of the Southern Oscillation, pp. 151–174. Cambridge University Press, Cambridge.

Petit, J.R.; Mounier, L.; Jouzel, J.; Koretkevitch, Y.S.; Kotlyakov, V.M.; Lorius, C. (1990). Palaeoclimatological and chronological implications of the Vostok core dust record. Nature 293: 56–58.

Pillans, R.B. (1983). Upper Quarternary marine terrace chronology and deformation, South Taranaki, New Zealand. Geology 11: 292–297.

Power, S.; Tseitkin, F.; Torok, S.; Lavery, B.; Dahni, R.; McAvaney, B. (1998). Australian temperature, Australian rainfall and the Southern Oscillation, 1910–1992: coherent variability and recent changes. Australian Meteorological Magazine 47: 85–101.

Royal Society of New Zealand (1994). Paleoclimates and climate modelling. Misc. Series 29. Royal Society of New Zealand, Wellington. 48 p.

Rayner, N.A.; Folland, C.K.; Parker, D.E.; Horton, B. (1995). A new Global Sea-Ice and Sea Surface Temperature (GISST) data set for 1903–1994 for forcing climate models. Internal Note 69. Hadley Centre, UK Meteorological Office, Bracknell. 13 p.

Ruddell, A. (1996). Recent glacier and climate change in the New Zealand Alps. Unpublished PhD thesis, University of Melbourne.

Salinger, M.J. (1988). New Zealand climate: Past and present. In: Climate Change – The New Zealand Response; Proceedings of a workshop in Wellington, March 29–30 1988, pp. 17–24. Ministry for the Environment, Wellington.

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Salinger, M.J.; Allan, R.; Bindoff, N.; Hannah, J.; Lavery, B.; Lin, Z.; Lindesay, J.; Nicholls, N.; Plummer, N.; Torok, S. (1996). Observed variability and change in climate and sea levels in Australia, New Zealand and the South Pacific. In: Bouma, W.J.; Pearman, G.I.; Manning, M.R. (eds). Greenhouse – Coping with Climate Change, pp. 100–126. CSIRO Publishing, Collingwood.

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Prepared by David Wratt, Jim Salinger, Rob Bell, Drew Lorrey and Brett Mullan