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Climate Change

Our climate: What's in store?

Scientists say there is no longer any doubt that the Earth’s climate is warming. Despite the cooling effects of a strong La Niña, 2011 was globally the ninth warmest year since 1880, reinforcing a trend which shows that nine of the 10 warmest years on modern record happened after 2000.

New Zealand temperature records show an increase of around one degree over the last 100 years. Sea level rise is another indicator of warming temperatures. Recordings from Moturiki Island, off Mt Maunganui, show sea levels there have risen 11 centimetres since 1950, an average rise of 1.9 millimetres a year, which matches the average global increase.

This fact sheet will help you find out more about climate change and how it affects us in the Bay of Plenty.

Why is our climate changing?

The Intergovernmental Panel on Climate Change (IPCC) confirms that changes in our climate are very likely caused by increased volumes of greenhouse gases, such as carbon dioxide, nitrous oxide and methane, in the atmosphere.

Ordinarily, solar energy from the sun passes through the Earth's atmosphere, and is absorbed at the surface. As it warms, the surface emits infra-red radiation. Most of that radiation is absorbed by greenhouse gases in the atmosphere, but enough escapes it to balance the net incoming solar energy. Over the long term, this equilibrium keeps temperatures relatively stable.

But when the concentration of greenhouse gases in the atmosphere increases, more radiation is trapped, and some of it is re-directed back to the lower atmosphere and surface. This drives the climate to a new, warmer balance.

The most abundant greenhouse gases are water vapour, carbon dioxide, nitrous oxide, methane and ozone. The increase in carbon dioxide is mainly the result of our burning more fossil fuels, such as petroleum and coal, even as we fell more and more forests, which would otherwise have helped absorb those gases.

In New Zealand, nearly half of our greenhouse gas emissions – mostly methane and nitrous oxides – come from livestock and fertiliser use.

For more information about climate change and New Zealand's overall approach see www.climatechange.govt.nz.  For inquiries regarding climate change and the New Zealand Emissions Trading Scheme, email climatechange@mfe.govt.nz or phone 0800 CLIMATE [0800 254 628].

What does this mean for our weather?

As this century unfolds, the Bay of Plenty climate will change. As temperatures rise, scientists expect New Zealand’s wind patterns to shift, which will also affect our future rainfall.

In 2011, Bay of Plenty Regional Council asked the National Institute of Water and Atmospheric Research (NIWA) to update its earlier 2003 climate change report for the region, incorporating a wealth of new information from more accurate climate models and projections.  Read here for key information about how scientists made their climate projections for the Bay of Plenty.

How the Bay of Plenty weather will change?

Temperatures

Temperatures will rise over the rest of this century.

  • By 2040, the average annual temperature will be1.2°C warmer than it was in 1990.
  • By 2090, it will be between 2.7ºC (mid-emission scenarios) and 3.6°C warmer (high emissions scenario).
  • Warming will be fairly uniform across the region.
  • Autumn and winter are projected to warm slightly more than summer and spring.

There will be more hot days by the end of the century.

 

days of 25°C or more (based on mid-range scenario)

Now

By 2040

By 2090

Rotorua

About 12 days a year

About 25 days a year

About 50 days a year

Tauranga

About 22 days a year

About 42 days a year

About 70 days a year

Whakatane

About 22 days a year

About 47 days a pear

About 80 days a year

Opotiki

About 10 days a year

About 26 days a year

About 60 days a year

Rain

Rain is likely to fall more heavily in future

The warmer air gets, the more moisture it can hold - about seven or eight percent more for each degree of warming - so rain is likely to fall more heavily in future.

The region will get roughly the same average annual rainfall in 2090 as it does now, but rain may fall at different times. For instance, winters are expected to get drier as the century unfolds; by 2090, coastal and south-eastern areas may receive 10 percent less rain than they do now. On the other hand, summer rainfall is projected to increase – particularly inland – and to become more variable. We may see a sharp year-to-year contrast of either very dry summers, or very wet ones.

Based on mid-range scenario

What is considered to be 
a 1-in-50-year event

The estimated frequency in the future

By 2040

By 2090

Whakarewarewa

160mm rainfall in 24 hours

1-in-33-year event

1-in-18-year event

Tauranga

200mm rainfall in 24 hours

1-in-34-year event

1-in-20-year event

Whakatane

150mm rainfall in 24 hours

1-in-29-year event

1-in-16-year event

Wind

More easterly winds during summer - more westerlies during winter

By analysing historical weather maps that have produced extreme winds in the past, and comparing them against the sort of maps we might expect in a warmer climate, scientists calculate that extreme winds may be less frequent during future summers, but more common during winters.

Frosts

There will be fewer frosts

By 2090, frosts will be a rare thing in the Bay of Plenty. At present, Ōpōtiki gets around five frosts a year, while Rotorua may get 20. By the end of the century, Rotorua is projected to experience frost just once or twice a year – none at all in some years. Other locations may get perhaps one frost every three years. There will be fewer cold nights.

 

 

The estimated frequency of frost days   (based on mid-range scenario)

Now

By 2040

By 2090

Rotorua

About 20 days a year

Around 8 - 9 days a year

Around 1 - 2 days a year

Katikati

About 11 days a year

Around 3 - 4 days a year

Around once in every 3 years

Te Puke

About 7 days a year

Around 1 - 2 days a year

Around once in every 5 years

Opotiki

About 5 days a year

Around once a year

Around once in every 10 years

Sea level

Sea-levels may rise between 50 cm and 80 cm

There is some uncertainty around the likely rate of sea-level rise this century, so scientists can only estimate a range of possible increases. Current predictions are for a sea-level rise of between 50 centimetres and 80 centimetres by the 2090s.

However, scientists can’t rule out the increase in sea-level could be more than a metre by 2100, which should at least be considered in planning and development. They expect sea-levels to go on rising for at least a few centrueis after 2100. That means new coastal development should factor in rises of between one and two metres to avoid future risks.

The Intergovernmental Panel on Climate Change (IPCC) will release updated sea level rise projections in its next assessment report, due in late 2013.

For more information