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Greenhouse warming still on



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Ros Kelly Minister for the Arts, Sport, the Environment, Tourism and Territories

G r e e n h o u s e W a r m i n g S t i l l O n

Recent estimates of global warming as a result of the greenhouse effect were reaffirmed at an international meeting of more than a hundred climate scientists from 47 countries ju st concluded in Guangzhou, China.

"On the basis of new modelling results, the IPCC group has reaffirmed its earlier best estimate of a 0.3 degrees celcius per decade global warming due to the greenhouse effect if there is no policy intervention to reduce greenhouse gas emissions", the Minister for the Arts, Sport, the Environment and Territories, Mrs Ros Kelly said today.

"These latest scientific findings reinforce the importance of the Government’s interim planning target of stabilising emissions of greenhouse gases by the year 2000 and reducing them by 20 per cent by 2005", Mrs Kelly said.

Mrs Kelly was commenting on the major conclusions of an updated scientific assessment of climate change by the Science Working Group of the

Intergovernmental Panel on Climate Change (IPCC).

The scientists’ assessment will be formally reviewed by the IPCC, a joint body of the World Meteorological Organisation and the United Nations Environment Programme, at its next plenary session in February.

The IPCC Working Group noted th a t the cooling effect of sulphur emissions in the northern hemisphere and stratospheric ozone depletion can be expected to offset global warming over the next few decades.

While partially offsetting greenhouse warming, sulphur emissions are also responsible for the major problems of acid rain in many parts of the world and other adverse environmental impacts.

The scientists noted th a t there are many uncertainties in their predictidhs particularly with regard to the timing, magnitude and regional patterns of climate change due to incomplete understanding.

The meeting in Guangzhou took account of all the new research on climate change since the IPCC’s First Assessment Report in 1990. That report triggered the intergovernmental negotiations on a climate change convention which is expected to be ready for signature at the United Nations Conference on Environment and Development in June 1992. More than 300 scientists worldwide have been involved in the writing and peer review of the new results.

Mrs Kelly said th at the new report has been significantly influenced by the work of the Australian climate research community who held a workshop in Melbourne in December to review early drafts of the Supplementary Report and a large volume of supporting material.

The meeting in Guangzhou was chaired by Sir John Houghton, the recently retired Director-General of the UK Meteorological Office and one of the world’s leading climate scientists.

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The A ustralian delegation to the Guangzhou meeting consisted of Dr J.W. Zillman, Commonwealth Director of Meteorology, Dr G.B. Tucker, Chief of the CSIRO Division of Atmospheric Research and Mr P. Cheng of the Climate Change and Environmental Liaison Branch of the Department of the Arts, Sport, the Environment and Territories.

A summary of the major conclusions of the Supplementary Report as released on 17 January by the Working Group Chairman is attached.

Mrs Kelly will be giving a speech on Greenhouse at the National Convention Centre (Canberra) on Monday 20 January 1992 at 9.30 a.m.

F urther Information:

Mr David Lording, Minister’s office, ph (06) 277 7640 (w) (06) 281 1924 (h) Dr J.W. Zillman, Bureau of Meteorology, Melbourne, ph (03) 669 4558

17 Jan u ary 1992 4/92

SCIENCE ASSESSMENT MEETING OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) IN GUANGZHOU, CHINA 13 -1 5 JANUARY 1992

The Science Working Group of the IPCC held its third session in Guangzhou, China at the invitation of the State Meteorological Administration of China from 13 to 15 January 1992 under the chairmanship of Sir John Houghton of the United Kingdom. Excellent facilities for the meeting were provided by the

Chinese hosts. 130 scientists from 47 countries and 13 organisations attended. Two thirds of the national delegations were from developing countries.

Papers prepared and reviewed by more than 300 experts from many countries were considered by the working group. A supplementary report updating the 1990 Scientific Assessment of the IPCC was prepared to assist the governments negotiating the International Convention on Climate Change which will be considered at the United Nations Conference on Environment and Development (UNCED) to be held in Brazil in June 1992. A summary of the major conclusions of the supplementary report follows.

MAJOR CONCLUSIONS

Findings of scientific research since 1990 do not affect our fundamental understanding of the science of the greenhouse effect and either confirm or do not justify alteration of the major conclusions of the first IPCC Scientific Assessment, in particular the following:

• "emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: carbon dioxide, methane, chlorofluorocarbons, and nitrous oxide"

• "The evidence from the modelling studies, from observations and the sensitivity analyses indicate t h a t t h e sensitivity of global mean surface temperature to doubling CO is unlikely to lie outside the range 1.5° to 4.5°C"

• "there are many uncertainties in our predictions particularly with regard to the timing, magnitude and regional patterns of climate change due to our incomplete understanding"

• "global mean surface air temperature has increased by 0.3 to 0. 6°C over the last 100 years" •

• "the size of this warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability. Thus the observed increase could be largely due to this natural

variability; alternatively this variability and other human factors could have offset a still larger human-induced greenhouse warming" ,

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9 *the unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more."

There are also a number of significant new findings and conclusions which we summarize as follows:

Gases and aerosols

• Depletion of ozone in the lower stratosphere in the middle and high latitudes is believed to have approximately offset the radiative forcing contribution of chlorofluorocarbons over the last decade or so.

• The cooling effect of sulphur emissions-may have offset a significant part of the greenhouse warming in the northern hemisphere during the past several decades. Although this phenomenon was recognized in the 1990 report, significant progress has been made in quantifying its effect.

• Although the Global Warming Potential (GWP) remains a useful concept, there is increased uncertainty in its calculation especially regarding the indirect effect. Whilst indirect GWPs are likely to be significant for some gases, the numerical estimates in this Supplementary Report

are limited to direct GWPs.

• whilst the rates of increase in the atmospheric concentrations of most greenhouse gases have continued to grow or remain steady, these of methane and some halogen compounds have slowed.

• Some data indicate lower emissions of methane from rice paddies than previously estimated.

Scenarios

• Steps have been taken towards a more comprehensive analysis of the dependence of future greenhouse gas emissions on socioeconomic assumptions and projections. A set of updated scenarios has been developed which describes a wide

range of possible future emissions in the absence of policy intervention, for use in modelling studies.

Modelling

• Climate models have continued to improve in both their physical realism and their ability to simulate present climate on large scales, and new techniques have been developed for the simulation of regional climate. •

• Transient (time-dependent) simulations with coupled ocean- atmosphere models (CGCMs), in which both aerosols and ozone changes have not been included, suggest a rate of global warming that is consistent,Qwithin the range of uncertainties, with the 0.3 C per decade warming rate quoted by IPCC (1990) for Scenario A of greenhouse gas emissions.

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• The large scale geographical patterns of wanning produced by the transient model runs with CGCMs are generally similar to the patterns produced by the earlier equilibrium models except that the transient simulations show reduced warming over the northern North Atlantic and the southern oceans near Antarctica.

• CGCMs are capable of reproducing many features of atmospheric variability on intra-decadal time scales.

• Our understanding of some climate feedbacks and their incorporation in the models has improved. In particular, there has been some clarification of the role of upper tropospheric water vapour. The role of other processes, in particular cloud effects, remains unresolved.

Climate Observations r

The anomalously high global mean temperatures of the late 1980s have continued into 1990 and 1991 which are the warmest years in the record.

Average warming over parts of the northern hemisphere mid­ latitude continents has been found to be largely characterized by increases in minimum (nighttime) father than maximum (daytime) temperatures.

Radiosonde data indicate that the lower troposphere has warmed over recent decades. Since meaningful trends cannot be assessed over periods as short as a decade, the widely reported disagreements between decadal temperature trends given by satellite data of air temperature and surface data

cannot be confirmed because the trends are statistically indistinguishable.

The volcanic eruption of M t . Finatubo in 1991 is expected to lead to transitory stratospheric warming. With less certainty, because of other natural influences, surface and tropospheric cooling may occur during the next few years.

Average warming over the northern hemisphere has not been uniform, with marked seasonal and geographic variations; this warming has been especially slow or absent over the extratropical north west Atlantic.

The consistency between observations of global .temperature changes over the past century and model simulations of the warming due to greenhouse gases over the same period, is improved if allowance is made for the increasing evidence of a cooling effect due to sulphate aerosols and

stratospheric ozone depletion.

The above conclusions have implications for future projections of global warming and somewhat modify the estimated rate of warming of 0.3°C per decade for the greenhouse gas emissions Scenario A of the IPCC 1990 Report. Due to sulphur emissions, this warming rate is likely to be reduced significantly in the Northern Hemisphere, by an amount dependent on the future

magnitude and regional distribution of the emissions. Because sulphate aerosols are very shortlived in the atmosphere their effect on global warming rapidly"adjusts to increases or decreases in emissions. It should also be noted that while partially offsetting the greenhouse warming, the sulphur

emissions are also responsible for acid rain and other environmental effects. There is a further small net reduction likely in the rate of global warming during the next few decades due to decreases in stratospheric ozone and increases in tropospheric ozone.

Research carried out since the 1990 IPCC Assessment has served to improve our appreciation of key uncertainties. There is a continuing need for increased monitoring and research into climate processes and modelling. This must involve, in particular, strengthened international collaboration through the

World Climate Research Programme (WCRP), the International Geosphere Biosphere Programme (IGBP) and the Global Climate Observing System (GCOS).