Future Climate Scenarios for New Zealand David Wratt Chief Scientist Climate, NIWA, Wellington E-Workshop on Climate Change Related Research for the Forestry Sector 16 December 2010

Talk Outline Reminder: Future climate will be the sum of natural plus anthropogenic influences Scenarios, and why we use them Recent changes Future scenarios - Global and NZ Implications of global changes ? Summary

Climate = Natural variation + human effects Easterling and Wehner, Geophysical Research Letters, 2009: “The climate over the 21st century can and likely will produce periods of a decade or two where the globally averaged surface air temperature shows no trend or even slight cooling in the presence of long-term warming” Keenlyside et al, 2008 - Over the next decade “Natural climate variations in the N Atlantic and tropical Pacific {may} temporarily offset the projected global warming” Smith et al, 2007 - “Our system predicts that internal variability will partially offset the anthropogenic global warming signal for the next few years. However, climate will continue to warm,with at least half of the years after 2009 predicted to exceed the warmest year currently on record Lean and Rind, 2009 3 3

Scenarios: What and why ? Scenario: “A plausible and often simplified description of how the future may develop, based on a coherent and internally consistent set of assumptions about driving forces and key relationships” (IPCC AR4 Synthesis Report) We don’t know what the future greenhouse gas emissions trajectory will be since it depends on future political, social and economic developments Climate scenarios, based on emissions scenarios plus climate projections, help governments consider policy options, and help potentially affected groups consider adaptation options.

Setting the scene: Recent global changes Source://data.giss.nasa.gov/gistemp/graphs/ Temperature (1880-2009) Temperature Anomaly (oC) -0.4 -0.2 0.0 0.2 0.4 0.6 1880 1900 1920 1940 1980 1960 2000 NASA GISS Annual Global Land-Ocean From Manning et al, Nature Geoscience, June 2010 Fossil Fuel CO2 emissions cf IPCC Scenarios http://nsidc.org/images/arcticseaicenews/20091005_Figure3.png End of summer Arctic Sea-ice (1979-2009) 5

Coming Century - 2 alternative scenarios High carbon world (SRES A2) high carbon world (SRES A2) Rapidly decarbonizing world rapidly decarbonising world Figures based on Meinshausen et al., Nature 2009 + Reisinger pers com

NZ scenarios: Changes in temperature (compared to 1980-99) (Courtesy Brett Mullan, NIWA) (Courtesy Brett Mullan, NIWA) °C °C

NZ scenarios: Changes in precipitation (compared to 1980-99) (Courtesy Brett Mullan, NIWA) (Courtesy Brett Mullan, NIWA)

NZ scenarios: Changes in precipitation (compared to 1980-99) (Courtesy Brett Mullan, NIWA) (Courtesy Brett Mullan, NIWA)

Other expected changes Enhanced westerlies Fewer frosts, more very hot days Extreme rainfall: Heavy rainfall likely to get heavier &/or more frequent for a mid-range scenario a 1-in-100 year event now could become a 1-in-50 year event by the end of the century Depth/duration/frequency guidance provided for preliminary assessments . Change to snow-lying duration at lower altitudes; glacier shrinkage More evaporation, increased risk of drought

What might projected changes mean for forestry production elsewhere around the Globe ? A1B: 2080-2099 Source: IPCC Technical Paper on Climate Change and Water Figure 2.8: Fifteen-model mean changes in (a) precipitation (%), (b) soil moisture content (%), (c) runoff (%), and (d) evaporation (%). To indicate consistency of sign of change, regions are stippled where at least 80% of models agree on the sign of the mean change. Changes are annual means for the scenario SRES A1B for the period 2080–2099 relative to 1980–1999. Soil moisture and runoff changes are shown at land points with valid data from at least ten models. [Based on WGI Figure 10.12] Drying of the subtropics, wetter poleward (10-20%) The globe becoming more tropical Increased frequency of droughts Dust-bowl = 10% drier for 10 years Increased frequency of heavy rainfalls (more intense cyclones..?)

Conclusions Scenarios are a useful “what-if” tool for considering policy options and potential impacts and adaptations Remember there will be year-to-year and decade-to-decade natural variability superimposed on scenarios of anthropogenic change. Climate scenarios for NZ project significant changes in temperature, seasonal precipitation, drought risk, and heavy rainfall / flood frequency later this century, especially for a “high carbon” emissions scenario. Changes to climate in other parts of the globe could be important for the NZ forest sector, if they inflence production by our “competitors”. NZ climate scientists can provide (and have provided) gridded climate projections for various scenarios, for use by forestry scientists who wish to explore implications for fire risk, forest growth, suitable species, disease and pest risk, …