1. 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

2. 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

3. 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, Over the next decade “Natural climate variations in the N Atlantic and tropical Pacific {may} temporarily offset the projected global warming”
Smith et al, “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

4. 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.

5. Setting the scene: Recent global changes
Source://data.giss.nasa.gov/gistemp/graphs/
Temperature ( )
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
End of summer Arctic
Sea-ice ( ) 5

6. 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 Reisinger pers com

7. NZ scenarios: Changes in temperature
(compared to )
(Courtesy Brett Mullan, NIWA)
(Courtesy Brett Mullan, NIWA) °C °C

8. NZ scenarios: Changes in precipitation
(compared to )
(Courtesy Brett Mullan, NIWA)
(Courtesy Brett Mullan, NIWA)

9. NZ scenarios: Changes in precipitation
(compared to )
(Courtesy Brett Mullan, NIWA)
(Courtesy Brett Mullan, NIWA)

10. 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

11. What might projected changes mean for forestry production elsewhere around the Globe ?
A1B:
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..?)

12. 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, …