绘制全球气候态时添加海岸线后刻度无法对应

问题遇到的现象和发生背景

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问题相关代码，请勿粘贴截图
import xarray as xr
import numpy as np
import netCDF4 as nc4
import pandas as pd
from cartopy.util import add_cyclic_point
import cartopy.crs as ccrs
import cartopy.mpl.geoaxes
import matplotlib.pyplot as plt
import matplotlib
import cartopy
matplotlib.rcParams['axes.unicode_minus']=False
matplotlib.rcParams['font.family'] = 'SimHei'

f1=xr.open_dataset(r'C:\sj\dc\hgt.mon.mean.nc')
lon=f1.lon
lat=f1.lat
f2=f1.hgt.sel(level=500,time='2008-01-01')
plt.figure(figsize=(16,8),dpi=200)
ax=plt.axes(projection=ccrs.PlateCarree(central_longitude=0))
f2,lon = add_cyclic_point(f2, coord=lon)
qs=ax.contourf(lon,lat,f2,levels=80,cmap='RdBu_r')
cs=ax.contour(lon,lat,f2)
plt.colorbar(qs)
ax.set_xticks(lon[::4])
ax.set_yticks([lat[i] for i in range(0,74,4)])
plt.show()
运行结果及报错内容
我的解答思路和尝试过的方法
我想要达到的结果

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